# `public_key`
[🔗](https://github.com/erlang/otp/blob/OTP-29.0.3/lib/public_key/src/public_key.erl#L25)

API module for public-key infrastructure.

Provides functions to handle public-key infrastructure, for details see
[public_key application](public_key_app.md).

> #### Note {: .info }
>
> All records used in this Reference Manual are generated from ASN.1
> specifications and are documented in the User's Guide. See
> [Public-key Records](public_key_records.md).

Use the following include directive to get access to the records and constant
macros described here and in the User's Guide:

```text
 -include_lib("public_key/include/public_key.hrl").
```

# `crl_reason`
*not exported* 

```erlang
-type crl_reason() ::
          unspecified | keyCompromise | cACompromise | affiliationChanged | superseded |
          cessationOfOperation | certificateHold | privilegeWithdrawn | aACompromise.
```

The reason that a certifcate has been revoked as define by RFC 5280.

# `bad_cert_reason`

```erlang
-type bad_cert_reason() ::
          cert_expired | invalid_issuer | invalid_signature | distinguished_name_not_permitted |
          name_not_permitted | missing_basic_constraint | invalid_key_usage | duplicate_cert_in_path |
          {key_usage_mismatch, term()} |
          {policy_requirement_not_met, term()} |
          {invalid_policy_mapping, term()} |
          {revoked, crl_reason()} |
          invalid_validity_dates |
          {revocation_status_undetermined, term()} |
          atom().
```

The reason that a certifcate gets rejected by the certificate path validation.

# `cert`

```erlang
-type cert() ::
          der_encoded() |
          #'OTPCertificate'{tbsCertificate :: term(), signatureAlgorithm :: term(), signature :: term()}.
```

An encoded or decode certificate.

# `cert_id`

```erlang
-type cert_id() :: {SerialNr :: integer(), issuer_name()}.
```

A certificate is identified by its serial-number and Issuer Name.

# `combined_cert`

```erlang
-type combined_cert() ::
          #cert{der :: public_key:der_encoded(),
                otp ::
                    #'OTPCertificate'{tbsCertificate :: term(),
                                      signatureAlgorithm :: term(),
                                      signature :: term()}}.
```

A record that can be used to provide the certificate on both the DER encoded and the OTP decode format.

Such a construct can be useful to avoid conversions and problems that can arise due to relaxed decoding rules.

# `issuer_name`

```erlang
-type issuer_name() :: {rdnSequence, [[#'AttributeTypeAndValue'{type :: term(), value :: term()}]]}.
```

The value of the issuer part of a certificate.

# `policy_node`

```erlang
-type policy_node() ::
          #{valid_policy := oid(),
            qualifier_set :=
                [#'UserNotice'{noticeRef :: term(), explicitText :: term()} | {uri, string()}],
            expected_policy_set := [oid()]}.
```

Certificate policy information.

# `public_key_info`

```erlang
-type public_key_info() ::
          {oid(), rsa_public_key() | #'ECPoint'{point :: term()} | dss_public_key(), key_params()}.
```

Information a certificates public key.

Possible oids: ?'rsaEncryption' | ?'id-RSASSA-PSS' | ?'id-ecPublicKey' | ?'id-Ed25519' | ?'id-Ed448' | ?'id-dsa'

# `asn1_type`

```erlang
-type asn1_type() :: atom().
```

ASN.1 type present in the Public Key applications ASN.1 specifications.

# `der_encoded`

```erlang
-type der_encoded() :: binary().
```

ASN.1 DER encoded entity.

# `digest_type`

```erlang
-type digest_type() :: crypto:sha2() | crypto:sha1() | legacy_digest_type() | none.
```

Hash function used to create a message digest

# `oid`

```erlang
-type oid() :: tuple().
```

Object identifier, a tuple of integers as generated by the `ASN.1` compiler.

# `custom_key_opts`

```erlang
-type custom_key_opts() :: [term()].
```

Can be provided together with a custom private key, that specifies a key fun, to
provide additional options understood by the fun.

# `dsa_private_key`

```erlang
-type dsa_private_key() ::
          #'DSAPrivateKey'{version :: term(),
                           p :: term(),
                           q :: term(),
                           g :: term(),
                           y :: term(),
                           x :: term()}.
```

ASN.1 defined private key format for the DSA algorithm.

# `dsa_public_key`

```erlang
-type dsa_public_key() :: {dss_public_key(), #'Dss-Parms'{p :: term(), q :: term(), g :: term()}}.
```

ASN.1 defined public key format for the DSA algorithm.

# `dss_public_key`
*not exported* 

```erlang
-type dss_public_key() :: pos_integer().
```

ASN.1 defined public key format for the DSS algorithm (part of DSA key).

# `ecdsa_public_key`

```erlang
-type ecdsa_public_key() ::
          {#'ECPoint'{point :: term()},
           {namedCurve, oid()} |
           #'ECParameters'{version :: term(),
                           fieldID :: term(),
                           curve :: term(),
                           base :: term(),
                           order :: term(),
                           cofactor :: term()}}.
```

ASN.1 defined public key format for the ECDSA algorithm.

# `eddsa_private_key`

```erlang
-type eddsa_private_key() ::
          #'ECPrivateKey'{parameters :: {namedCurve, oid()},
                          version :: term(),
                          privateKey :: term(),
                          publicKey :: term(),
                          attributes :: term()}.
```

ASN.1 defined private key format for the EDDSA algorithm, possible oids: ?'id-Ed25519' | ?'id-Ed448'

# `eddsa_public_key`

```erlang
-type eddsa_public_key() :: {#'ECPoint'{point :: term()}, {namedCurve, oid()}}.
```

ASN.1 defined public key format for the EDDSA algorithm, possible oids: ?'id-Ed25519' | ?'id-Ed448'

# `public_key`

```erlang
-type public_key() ::
          rsa_public_key() |
          rsa_pss_public_key() |
          dsa_public_key() |
          ecdsa_public_key() |
          eddsa_public_key() |
          mldsa_public_key() |
          ml_kem_public_key() |
          slh_dsa_public_key().
```

Supported public keys

# `rsa_private_key`

```erlang
-type rsa_private_key() ::
          #'RSAPrivateKey'{version :: term(),
                           modulus :: term(),
                           publicExponent :: term(),
                           privateExponent :: term(),
                           prime1 :: term(),
                           prime2 :: term(),
                           exponent1 :: term(),
                           exponent2 :: term(),
                           coefficient :: term(),
                           otherPrimeInfos :: term()} |
          #{algorithm := rsa, encrypt_fun => fun()}.
```

ASN.1 defined private key format plain RSA algorithm or customization fun.

# `rsa_pss_private_key`

```erlang
-type rsa_pss_private_key() ::
          {#'RSAPrivateKey'{version :: term(),
                            modulus :: term(),
                            publicExponent :: term(),
                            privateExponent :: term(),
                            prime1 :: term(),
                            prime2 :: term(),
                            exponent1 :: term(),
                            exponent2 :: term(),
                            coefficient :: term(),
                            otherPrimeInfos :: term()},
           #'RSASSA-PSS-params'{hashAlgorithm :: term(),
                                maskGenAlgorithm :: term(),
                                saltLength :: term(),
                                trailerField :: term()}}.
```

ASN.1 defined private key format the RSSASSA-PSS algorithm or customization fun.

# `rsa_pss_public_key`

```erlang
-type rsa_pss_public_key() ::
          {rsa_public_key(),
           #'RSASSA-PSS-params'{hashAlgorithm :: term(),
                                maskGenAlgorithm :: term(),
                                saltLength :: term(),
                                trailerField :: term()}}.
```

ASN.1 defined public key format for the RSSASSA-PSS algorithm.

# `rsa_public_key`

```erlang
-type rsa_public_key() :: #'RSAPublicKey'{modulus :: term(), publicExponent :: term()}.
```

ASN.1 defined public key format for plain RSA algorithm.

# `pem_entry`

```erlang
-type pem_entry() ::
          {pki_asn1_type(),
           DerOrDerEncrypted :: binary(),
           not_encrypted |
           {Cipher :: iodata(),
            Salt ::
                binary() |
                {#'PBEParameter'{salt :: term(), iterationCount :: term()}, digest_type()} |
                #'PBES2-params'{keyDerivationFunc :: term(), encryptionScheme :: term()}}}.
```

Possible `Ciphers` are "RC2-CBC" | "DES-CBC" | "DES-EDE3-CBC" `Salt` could be generated with
[`crypto:strong_rand_bytes(8)`](`crypto:strong_rand_bytes/1`).

# `pki_asn1_type`

```erlang
-type pki_asn1_type() ::
          'Certificate' | 'RSAPrivateKey' | 'RSAPublicKey' | 'SubjectPublicKeyInfo' | 'DSAPrivateKey' |
          'DHParameter' | 'PrivateKeyInfo' | 'CertificationRequest' | 'ContentInfo' |
          'CertificateList' | 'ECPrivateKey' | 'OneAsymmetricKey' | 'EcpkParameters'.
```

ASN.1 type that can be found in PEM files that can be decode by the public_key application.

# `cert_opt`

```erlang
-type cert_opt() ::
          {digest, digest_type()} |
          {key,
           {namedCurve, oid()} |
           #'ECParameters'{version :: term(),
                           fieldID :: term(),
                           curve :: term(),
                           base :: term(),
                           order :: term(),
                           cofactor :: term()} |
           {rsa, Size :: pos_integer(), Prime :: pos_integer()} |
           private_key()} |
          {validity, {From :: erlang:timestamp(), To :: erlang:timestamp()}} |
          {extensions, [#'Extension'{extnID :: term(), critical :: term(), extnValue :: term()}]}.
```

Options to customize generated test certificates

# `chain_opts`

```erlang
-type chain_opts() :: #{root := [cert_opt()], intermediates => [[cert_opt()]], peer := [cert_opt()]}.
```

Certificate customize options for diffrent parts of the certificate test chain.

# `conf_opt`

```erlang
-type conf_opt() ::
          {cert, der_encoded()} |
          {key, private_key() | {both, public_key(), private_key()}} |
          {cacerts, [der_encoded()]}.
```

Configuration options for the generated certificate test chain.

# `ecdsa_private_key`

```erlang
-type ecdsa_private_key() ::
          #'ECPrivateKey'{version :: term(),
                          privateKey :: term(),
                          parameters :: term(),
                          publicKey :: term(),
                          attributes :: term()}.
```

ASN.1 defined private key format for the ECDSA algorithm.

# `key_params`

```erlang
-type key_params() ::
          'NULL' |
          #'RSASSA-PSS-params'{hashAlgorithm :: term(),
                               maskGenAlgorithm :: term(),
                               saltLength :: term(),
                               trailerField :: term()} |
          {namedCurve, oid()} |
          #'ECParameters'{version :: term(),
                          fieldID :: term(),
                          curve :: term(),
                          base :: term(),
                          order :: term(),
                          cofactor :: term()} |
          #'Dss-Parms'{p :: term(), q :: term(), g :: term()}.
```

ASN.1 defined parameters for public key algorithms.

# `legacy_digest_type`
*not exported* 

```erlang
-type legacy_digest_type() :: md5 | md2.
```

# `ml_kem_private_key`
*not exported* 

```erlang
-type ml_kem_private_key() ::
          #'ML-KEMPrivateKey'{algorithm :: crypto:kem(), seed :: binary(), expandedkey :: binary()}.
```

ML-KEM private key

# `ml_kem_public_key`
*not exported* 

```erlang
-type ml_kem_public_key() :: #'ML-KEMPublicKey'{algorithm :: crypto:kem(), key :: binary()}.
```

ML-KEM public key

# `mldsa_private_key`

```erlang
-type mldsa_private_key() ::
          #'ML-DSAPrivateKey'{algorithm :: crypto:mldsa(), seed :: binary(), expandedkey :: binary()}.
```

ML-DSA private key

# `mldsa_public_key`

```erlang
-type mldsa_public_key() :: #'ML-DSAPublicKey'{algorithm :: crypto:mldsa(), key :: binary()}.
```

ML-DSA public key

# `private_key`

```erlang
-type private_key() ::
          rsa_private_key() |
          rsa_pss_private_key() |
          dsa_private_key() |
          ecdsa_private_key() |
          eddsa_private_key() |
          mldsa_private_key() |
          ml_kem_private_key() |
          slh_dsa_private_key() |
          #{algorithm := slh_dsa | mldsa | eddsa | rsa_pss_pss | ecdsa | rsa | dsa, sign_fun => fun()}.
```

Supported private keys

# `slh_dsa_private_key`

```erlang
-type slh_dsa_private_key() :: #'SLH-DSAPrivateKey'{algorithm :: crypto:slh_dsa(), key :: binary()}.
```

SLH-DSA private key

# `slh_dsa_public_key`

```erlang
-type slh_dsa_public_key() :: #'SLH-DSAPublicKey'{algorithm :: crypto:slh_dsa(), key :: binary()}.
```

SLH-DSA public key

# `der_decode`
*since OTP R14B* 

```erlang
-spec der_decode(Asn1Type, Der) -> Entity
                    when Asn1Type :: asn1_type(), Der :: der_encoded(), Entity :: term().
```

Decodes a public-key ASN.1 DER encoded entity.

# `der_encode`
*since OTP R14B* 

```erlang
-spec der_encode(Asn1Type, Entity) -> Der
                    when Asn1Type :: asn1_type(), Entity :: term(), Der :: binary().
```

Encodes a public-key entity with ASN.1 DER encoding.

# `cacerts_clear`
*since OTP 25.0* 

```erlang
-spec cacerts_clear() -> boolean().
```

Clears any loaded CA certificates, returns true if any was loaded.

# `cacerts_get`
*since OTP 25.0* 

```erlang
-spec cacerts_get() -> [combined_cert()].
```

Returns the trusted CA certificates if any are loaded, otherwise uses
`cacerts_load/0` to load them. The function fails if no `cacerts` could be
loaded.

# `cacerts_load`
*since OTP 25.0* 

```erlang
-spec cacerts_load() -> ok | {error, Reason :: term()}.
```

Loads the OS supplied trusted CA certificates.

This can be overridden by setting the `cacerts_path`
environment key of the `public_key` application with
the location of an alternative certificate.
You can set it via the command line as:

    erl -public_key cacerts_path '"/path/to/certs.pem"'

Use it with care. It is your responsibility to ensure
that the certificates found in this alternative path
can be trusted by the running system.

# `cacerts_load`
*since OTP 25.0* 

```erlang
-spec cacerts_load(File :: file:filename_all()) -> ok | {error, Reason :: term()}.
```

Loads the trusted CA certificates from a file.

# `pkix_decode_cert`

```erlang
-spec pkix_decode_cert(Cert, Type) ->
                          #'Certificate'{toBeSigned :: term(),
                                         algorithmIdentifier :: term(),
                                         signature :: term()} |
                          #'OTPCertificate'{tbsCertificate :: term(),
                                            signatureAlgorithm :: term(),
                                            signature :: term()}
                          when Cert :: der_encoded(), Type :: plain | otp | relaxed.
```

Decodes an ASN.1 DER-encoded PKIX certificate.

Option `otp` uses the customized ASN.1 specification OTP-PKIX.asn1 for
decoding and also recursively decode most of the standard parts.

Option `relaxed` is similar to option `otp` but also allows for empty
RDNs in issuer and subject.

# `pkix_encode`
*since OTP R14B* 

```erlang
-spec pkix_encode(Asn1Type, Entity, Type) -> Der
                     when
                         Asn1Type :: asn1_type(),
                         Entity :: term(),
                         Type :: otp | plain,
                         Der :: der_encoded().
```

DER encodes a PKIX x509 certificate or part of such a certificate.

This function must be used for encoding certificates or parts of
certificates that are decoded/created in the `otp` format, whereas for
the plain format this function directly calls
[`der_encode/2`](`der_encode/2`).

> #### Note {: .info }
>
> Subtle ASN-1 encoding errors in certificates may be worked around when
> decoding, this may have the affect that the encoding a certificate back to DER
> may generate different bytes then the supplied original.

# `pkix_hash_type`
*since OTP 23.0* 

```erlang
-spec pkix_hash_type(HashOid :: oid()) -> DigestType :: digest_type().
```

Translates OID to Erlang digest type

# `pkix_is_fixed_dh_cert`
*since OTP R14B* 

```erlang
-spec pkix_is_fixed_dh_cert(Cert) -> boolean() when Cert :: cert().
```

Checks if a certificate is a fixed Diffie-Hellman certificate.

# `pkix_is_issuer`
*since OTP R14B* 

```erlang
-spec pkix_is_issuer(CertorCRL, IssuerCert) -> boolean()
                        when
                            CertorCRL ::
                                cert() |
                                #'CertificateList'{toBeSigned :: term(),
                                                   algorithmIdentifier :: term(),
                                                   signature :: term()},
                            IssuerCert :: cert().
```

Checks if `IssuerCert` issued `Cert`.

# `pkix_is_self_signed`
*since OTP R14B* 

```erlang
-spec pkix_is_self_signed(Cert) -> boolean() when Cert :: cert().
```

Checks if a certificate is self-signed.

# `pkix_issuer_id`
*since OTP R14B* 

```erlang
-spec pkix_issuer_id(Cert, IssuedBy) -> {ok, ID :: cert_id()} | {error, Reason}
                        when Cert :: cert(), IssuedBy :: self | other, Reason :: term().
```

Returns the x509 certificate issuer id, if it can be determined.

# `pkix_normalize_name`
*since OTP R14B* 

```erlang
-spec pkix_normalize_name(Issuer) -> Normalized
                             when Issuer :: issuer_name() | der_encoded(), Normalized :: issuer_name().
```

Normalizes an issuer name so that it can be easily compared to another issuer
name.

# `pkix_path_validation`
*since OTP R16B* 

```erlang
-spec pkix_path_validation(Cert, CertChain, Options) ->
                              {ok, {PublicKeyInfo, ConstrainedPolicyNodes}} |
                              {error, {bad_cert, Reason :: bad_cert_reason()}}
                              when
                                  Cert :: cert() | combined_cert() | atom(),
                                  CertChain :: [cert() | combined_cert()],
                                  Options ::
                                      [{max_path_length, integer()} | {verify_fun, {fun(), term()}}],
                                  PublicKeyInfo :: public_key_info(),
                                  ConstrainedPolicyNodes :: [policy_node()].
```

Performs a basic path validation according to
[RFC 5280.](http://www.ietf.org/rfc/rfc5280.txt)

However, CRL validation is done separately by [pkix_crls_validate/3
](`pkix_crls_validate/3`)and is to be called from the supplied
`verify_fun`. The policy tree check was added in OTP-26.2 and if the
certificates include policies the constrained policy set with
potential qualifiers will be returned, these values are derived from
the policy tree created as part of the path validation algorithm. The
constrained set can be constrained only by the Certificate Authorities
or also by the user when the option `policy_set` is provided to this
function. The qualifiers convey information about the valid policy and
is intended as information to end users.

Available options:

- **\{verify_fun, \{fun(), UserState::term()\}** - The fun must be
  defined as:

  ```erlang
  fun(OtpCert :: #'OTPCertificate'{},
      Event :: {bad_cert, Reason :: bad_cert_reason() | {revoked, atom()}} |
               {extension, #'Extension'{}},
      UserState :: term()) ->
  	{valid, UserState :: term()} |
  	{valid_peer, UserState :: term()} |
  	{fail, Reason :: term()} |
  	{unknown, UserState :: term()}.
  ```

  or as:

  ```erlang
  fun(OtpCert :: #'OTPCertificate'{},
      DerCert :: der_encoded(),
      Event :: {bad_cert, Reason :: bad_cert_reason() | {revoked, atom()}} |
               {extension, #'Extension'{}},
      UserState :: term()) ->
	{valid, UserState :: term()} |
	{valid_peer, UserState :: term()} |
	{fail, Reason :: term()} |
	{unknown, UserState :: term()}.
  ```

  The verify callback can have 3 or 4 arguments in case the DER encoded
  version is needed by the callback.

  If the verify callback fun returns `{fail, Reason}`, the verification process
  is immediately stopped. If the verify callback fun returns
  `{valid, UserState}`, the verification process is continued. This can be used
  to accept specific path validation errors, such as `selfsigned_peer`, as well
  as verifying application-specific extensions. If called with an extension
  unknown to the user application, the return value `{unknown, UserState}` is to
  be used.

  > #### Note {: .note }
  > If you need the DER encoded version of the certificate and have
  > the OTP decoded version encoding it back can fail to give the correct result,
  > due to work arounds for common misbehaving encoders. So it is recommended
  > to call `pkix_path_validation` with `Cert` and `CertChain` arguments as
  >  `der_encoded() | #cert{}` and `[der_encoded() | #cert{}]`. Also note
  > that the path validation itself needs both the encoded and the
  > decoded version of the certificate.

  > #### Warning {: .warning }
  >
  > Note that user defined custom `verify_fun` may alter original path
  > validation error (e.g `selfsigned_peer`). Use with caution.

- **\{max_path_length, integer()\}** - The `max_path_length` is the maximum
  number of non-self-issued intermediate certificates that can follow the peer
  certificate in a valid certification path. So, if `max_path_length` is 0, the
  PEER must be signed by the trusted ROOT-CA directly, if it is 1, the path can
  be PEER, CA, ROOT-CA, if it is 2, the path can be PEER, CA, CA, ROOT-CA, and
  so on.

- **\{policy_set, \[oid()]\}**(Since OTP 26.2)  
  The set of policies that will be accepted, defaults to the special value
  `[?anyPolicy]` that will accept all policies.

- **\{explicit_policy, boolean()\}**(Since OTP 26.2)  
  Explicitly require that each certificate in the path must include at least one
  of the certificate policies in the `policy_set`.

- **\{inhibit_policy_mapping, boolean()\}**(Since OTP 26.2)  
  Prevent policies to be mapped to other policies.

- **\{inhibit_any_policy, boolean()\}**(Since OTP 26.2)  
  Prevent the special policy `?anyPolicy` from being accepted.

Explanations of reasons for a bad certificate:

- **cert_expired** - Certificate is no longer valid as its expiration date has
  passed.

- **invalid_issuer** - Certificate issuer name does not match the name of the
  issuer certificate in the chain.

- **invalid_signature** - Certificate was not signed by its issuer certificate
  in the chain.

- **distinguished_name_not_permitted** - Subject Name does not adhere to name constraints
  which is mandatory in RFC 5280.

- **name_not_permitted** - Subject Alternative Name does not adhere to name constraints,
  which is optional in RFC 5280.

- **missing_basic_constraint** - Certificate, required to have the basic
  constraints extension, does not have a basic constraints extension.

- **invalid_key_usage** - Certificate key is used in an invalid way according to
  the key-usage extension.

- **\{revoked, crl_reason()\}** - Certificate has been revoked.

- **invalid_validity_dates** - The validity section of the X.509 certificate(s)
  contains invalid date formats not matching the RFC.

- **atom()** - Application-specific error reason that is to be checked by the
  `verify_fun`.

# `pkix_sign_types`
*since OTP R16B01* 

```erlang
-spec pkix_sign_types(AlgorithmId) -> {DigestType, SignatureType}
                         when
                             AlgorithmId :: oid(),
                             DigestType :: digest_type(),
                             SignatureType ::
                                 rsa | dsa | ecdsa | eddsa | crypto:mldsa() | crypto:slh_dsa().
```

Translates signature algorithm OID to Erlang digest and signature types.

The `AlgorithmId` is the signature OID from a certificate or a certificate
revocation list.

# `pkix_subject_id`
*since OTP 23.1* 

```erlang
-spec pkix_subject_id(Cert) -> ID when Cert :: cert(), ID :: cert_id().
```

Returns the X509 certificate subject id.

# `pkix_verify_hostname`
*since OTP 19.3* 

```erlang
-spec pkix_verify_hostname(Cert, ReferenceIDs) -> boolean()
                              when
                                  Cert :: cert(),
                                  ReferenceIDs ::
                                      [{uri_id | dns_id | ip | srv_id | atom() | oid(), string()} |
                                       {ip, inet:ip_address() | string()}].
```

# `pkix_verify_hostname`
*since OTP 19.3* 

```erlang
-spec pkix_verify_hostname(Cert, ReferenceIDs, Options) -> boolean()
                              when
                                  Cert :: cert(),
                                  ReferenceIDs ::
                                      [{uri_id | dns_id | ip | srv_id | atom() | oid(), string()} |
                                       {ip, inet:ip_address() | string()}],
                                  Options :: [{match_fun | fail_callback | fqdn_fun, fun()}].
```

This function checks that the _Presented Identifier_ (e.g hostname) in a peer
certificate is in agreement with at least one of the _Reference Identifier_ that
the client expects to be connected to.

The function is intended to be added as an extra client check of the
peer certificate when performing
[public_key:pkix_path_validation/3](`pkix_path_validation/3`)

See [RFC 6125](https://tools.ietf.org/html/rfc6125) for detailed information
about hostname verification. The
[User's Guide](using_public_key.md#verify_hostname) and
[code examples](using_public_key.md#verify_hostname_examples) describes this
function more detailed.

The option funs are described here:

- **`match_fun`**

  ```erlang
  fun(ReferenceId::ReferenceId() | FQDN::string(),
      PresentedId::{dNSName,string()} | {uniformResourceIdentifier,string() |
                   {iPAddress,list(byte())} | {OtherId::atom()|oid(),term()}})
  ```

  This function replaces the default host name matching rules. The fun should
  return a boolean to tell if the Reference ID and Presented ID matches or not.
  The match fun can also return a third value, value, the atom `default`, if the
  default matching rules shall apply. This makes it possible to augment the
  tests with a special case:

  ```text
  fun(....) -> true;   % My special case
     (_, _) -> default % all others falls back to the inherit tests
  end
  ```

  See `pkix_verify_hostname_match_fun/1` for a function that takes a protocol
  name as argument and returns a `fun/2` suitable for this option and
  [Re-defining the match operation](using_public_key.md#redefining_match_op) in
  the User's Guide for an example.

  > #### Note {: .info }
  >
  > Reference Id values given as binaries will be converted to strings, and ip
  > references may be given in string format that is "10.0.1.1" or
  > "1234::5678:9012" as well as on the format `t:inet:ip_address/0`

- **`fail_callback`** - If a matching fails, there could be circumstances when
  the certificate should be accepted anyway. Think for example of a web browser
  where you choose to accept an outdated certificate. This option enables
  implementation of such an exception but for hostnames. This `fun/1` is called
  when no `ReferenceID` matches. The return value of the fun (a `t:boolean/0`)
  decides the outcome. If `true` the the certificate is accepted otherwise it is
  rejected. See
  ["Pinning" a Certificate](using_public_key.md#pinning-a-certificate) in the
  User's Guide.

- **`fqdn_fun`** - This option augments the host name extraction from URIs and
  other Reference IDs. It could for example be a very special URI that is not
  standardised. The fun takes a Reference ID as argument and returns one of:

  - the hostname
  - the atom `default`: the default host name extract function will be used
  - the atom `undefined`: a host name could not be extracted. The
    pkix_verify_hostname/3 will return `false`.

  For an example, see
  [Hostname extraction](using_public_key.md#hostname_extraction) in the User's
  Guide.

# `pkix_verify_hostname_match_fun`
*since OTP 21.0* 

```erlang
-spec pkix_verify_hostname_match_fun(Protocol) -> Result when Protocol :: https, Result :: fun().
```

The return value of calling this function is intended to be used in the
`match_fun` option in `pkix_verify_hostname/3`.

The returned fun augments the verify hostname matching according to the specific
rules for the protocol in the argument.

> #### Note {: .info }
>
> Currently supported https fun will allow wildcard certificate matching as
> specified by the HTTP standard. Note that for instance LDAP have a different
> set of wildcard matching rules. If you do not want to allow wildcard
> certificates (recommended from a security perspective) or otherwise customize
> the hostname match the default match function used by ssl application will be
> sufficient.

# `pkix_crl_issuer`
*since OTP 17.5* 

```erlang
-spec pkix_crl_issuer(CRL) -> Issuer
                         when
                             CRL ::
                                 der_encoded() |
                                 #'CertificateList'{toBeSigned :: term(),
                                                    algorithmIdentifier :: term(),
                                                    signature :: term()},
                             Issuer :: issuer_name().
```

Returns the issuer of the `CRL`.

# `pkix_crl_verify`
*since OTP 17.5* 

```erlang
-spec pkix_crl_verify(CRL, Cert) -> boolean()
                         when
                             CRL ::
                                 der_encoded() |
                                 #'CertificateList'{toBeSigned :: term(),
                                                    algorithmIdentifier :: term(),
                                                    signature :: term()},
                             Cert :: cert().
```

Verify that `Cert` is the `CRL` signer.

# `pkix_crls_validate`
*since OTP R16B* 

```erlang
-spec pkix_crls_validate(OTPcertificate, DPandCRLs, Options) -> CRLstatus
                            when
                                OTPcertificate ::
                                    #'OTPCertificate'{tbsCertificate :: term(),
                                                      signatureAlgorithm :: term(),
                                                      signature :: term()},
                                DPandCRLs :: [DPandCRL],
                                DPandCRL :: {DP, {DerCRL, CRL}},
                                DP ::
                                    #'DistributionPoint'{distributionPoint :: term(),
                                                         reasons :: term(),
                                                         cRLIssuer :: term()},
                                DerCRL :: der_encoded(),
                                CRL ::
                                    #'CertificateList'{toBeSigned :: term(),
                                                       algorithmIdentifier :: term(),
                                                       signature :: term()},
                                Options :: [{atom(), term()}],
                                CRLstatus :: valid | {bad_cert, BadCertReason},
                                BadCertReason ::
                                    revocation_status_undetermined |
                                    {revocation_status_undetermined, Reason :: term()} |
                                    {revoked, crl_reason()}.
```

Performs CRL validation. It is intended to be called from the verify fun of
[pkix_path_validation/3 ](`pkix_path_validation/3`).

Available options:

- **\{update_crl, fun()\}** - The fun has the following type specification:

  ```erlang
   fun(#'DistributionPoint'{}, #'CertificateList'{}) ->
          #'CertificateList'{}
  ```

  The fun uses the information in the distribution point to access the latest
  possible version of the CRL. If this fun is not specified, Public Key uses the
  default implementation:

  ```text
   fun(_DP, CRL) -> CRL end
  ```

- **\{issuer_fun, \{fun(), UserState::term()\}\}** - The fun has the following type
  specification:

  ```erlang
  fun(#'DistributionPoint'{}, #'CertificateList'{},
      {rdnSequence,[#'AttributeTypeAndValue'{}]}, UserState::term()) ->
  	{ok, #'OTPCertificate'{}, [der_encoded]}
  ```

  The fun returns the root certificate and certificate chain that has signed the
  CRL.

  ```erlang
   fun(DP, CRL, Issuer, UserState) -> {ok, RootCert, CertChain}
  ```

- **\{undetermined_details, boolean()\}** - Defaults to false. When revocation
  status cannot be determined, and this option is set to true, details of why no
  CRLs where accepted are included in the return value.

# `pkix_dist_point`
*since OTP 17.5* 

```erlang
-spec pkix_dist_point(Cert) -> DistPoint
                         when
                             Cert :: cert(),
                             DistPoint ::
                                 #'DistributionPoint'{distributionPoint :: term(),
                                                      reasons :: term(),
                                                      cRLIssuer :: term()}.
```

Creates a distribution point for CRLs issued by the same issuer as `Cert`. Can
be used as input to `pkix_crls_validate/3`

# `pkix_dist_points`
*since OTP 17.5* 

```erlang
-spec pkix_dist_points(Cert) -> DistPoints
                          when
                              Cert :: cert(),
                              DistPoints ::
                                  [#'DistributionPoint'{distributionPoint :: term(),
                                                        reasons :: term(),
                                                        cRLIssuer :: term()}].
```

Extracts distribution points from the certificates extensions.

# `pkix_match_dist_point`
*since OTP 19.0* 

```erlang
-spec pkix_match_dist_point(CRL, DistPoint) -> boolean()
                               when
                                   CRL ::
                                       der_encoded() |
                                       #'CertificateList'{toBeSigned :: term(),
                                                          algorithmIdentifier :: term(),
                                                          signature :: term()},
                                   DistPoint ::
                                       #'DistributionPoint'{distributionPoint :: term(),
                                                            reasons :: term(),
                                                            cRLIssuer :: term()}.
```

Checks whether the given distribution point matches the Issuing Distribution
Point of the CRL, as described in RFC 5280.

If the CRL doesn't have an Issuing
Distribution Point extension, the distribution point always matches.

# `pkix_ocsp_validate`
*since OTP 27.0* 

```erlang
-spec pkix_ocsp_validate(Cert, IssuerCert, OcspRespDer, NonceExt, Options) ->
                            {ok, Details} | {error, {bad_cert, Reason}}
                            when
                                Cert :: cert(),
                                IssuerCert :: cert(),
                                OcspRespDer :: der_encoded(),
                                NonceExt :: undefined | binary(),
                                Options ::
                                    [{is_trusted_responder_fun, fun((combined_cert()) -> boolean)}],
                                Details :: list(),
                                Reason :: bad_cert_reason().
```

Perform OCSP response validation according to RFC 6960. Returns {'ok', Details} when OCSP
response is successfully validated and \{error, \{bad_cert, Reason\}\}
otherwise.

Available options:

- **\{is_trusted_responder_fun, fun()\}** - The fun has the following type
  specification:

  ```text
   fun(#cert{}) ->
  	  boolean()
  ```

  The fun returns the `true` if certificate in the argument is trusted. If this
  fun is not specified, Public Key uses the default implementation:

  ```text
   fun(_) -> false end
  ```

> #### Note {: .info }
>
> OCSP response can be provided without a nonce value - even if it was requested
> by the client. In such cases {missing, ocsp_nonce} will be returned
> in Details list.

# `short_name_hash`
*since OTP 19.0* 

```erlang
-spec short_name_hash(Name) -> string() when Name :: issuer_name().
```

Generates a short hash of an issuer name. The hash is returned as a string
containing eight hexadecimal digits.

The return value of this function is the same as the result of the commands
`openssl crl -hash` and `openssl x509 -issuer_hash`, when passed the issuer name
of a CRL or a certificate, respectively. This hash is used by the `c_rehash`
tool to maintain a directory of symlinks to CRL files, in order to facilitate
looking up a CRL by its issuer name.

# `compute_key`
*since OTP R16B01* 

```erlang
-spec compute_key(OthersECDHkey, MyECDHkey) -> SharedSecret
                     when
                         OthersECDHkey :: #'ECPoint'{point :: term()},
                         MyECDHkey ::
                             #'ECPrivateKey'{version :: term(),
                                             privateKey :: term(),
                                             parameters :: term(),
                                             publicKey :: term(),
                                             attributes :: term()},
                         SharedSecret :: binary().
```

Computes shared secret.

# `compute_key`
*since OTP R16B01* 

```erlang
-spec compute_key(OthersDHkey, MyDHkey, DHparms) -> SharedSecret
                     when
                         OthersDHkey :: crypto:dh_public(),
                         MyDHkey :: crypto:dh_private(),
                         DHparms ::
                             #'DHParameter'{prime :: term(),
                                            base :: term(),
                                            privateValueLength :: term()},
                         SharedSecret :: binary().
```

Computes shared secret.

# `dh_gex_group`
*since OTP 18.2* 

```erlang
-spec dh_gex_group(MinSize, SuggestedSize, MaxSize, Groups) -> {ok, {Size, Group}} | {error, term()}
                      when
                          MinSize :: pos_integer(),
                          SuggestedSize :: pos_integer(),
                          MaxSize :: pos_integer(),
                          Groups :: undefined | [{Size, [Group]}],
                          Size :: pos_integer(),
                          Group :: {G, P},
                          G :: pos_integer(),
                          P :: pos_integer().
```

Selects a group for Diffie-Hellman key exchange with the key size in the range
`MinSize...MaxSize` and as close to `SuggestedSize` as possible. If
`Groups == undefined` a default set will be used, otherwise the group is
selected from `Groups`.

First a size, as close as possible to SuggestedSize, is selected. Then one group
with that key size is randomly selected from the specified set of groups. If no
size within the limits of `MinSize` and `MaxSize` is available,
`{error,no_group_found}` is returned.

The default set of groups is listed in `lib/public_key/priv/moduli`. This file
may be regenerated like this:

```text
	$> cd $ERL_TOP/lib/public_key/priv/
	$> generate
         ---- wait until all background jobs has finished. It may take several days !
	$> cat moduli-* > moduli
	$> cd ..; make
```

# `generate_key`
*since OTP R16B01* 

```erlang
-spec generate_key(DHparams | ECparams | RSAparams | MLDSA | SLHDSA) ->
                      DHkeys | ECkey | RSAkey | MLDSAKeys | SLHDSAKeys
                      when
                          DHparams ::
                              #'DHParameter'{prime :: term(),
                                             base :: term(),
                                             privateValueLength :: term()},
                          DHkeys :: {PublicDH :: binary(), PrivateDH :: binary()},
                          ECparams ::
                              {namedCurve, oid() | atom()} |
                              #'ECParameters'{version :: term(),
                                              fieldID :: term(),
                                              curve :: term(),
                                              base :: term(),
                                              order :: term(),
                                              cofactor :: term()},
                          ECkey ::
                              #'ECPrivateKey'{version :: term(),
                                              privateKey :: term(),
                                              parameters :: term(),
                                              publicKey :: term(),
                                              attributes :: term()},
                          RSAparams :: {rsa, Size, PubExp},
                          Size :: pos_integer(),
                          PubExp :: pos_integer(),
                          RSAkey ::
                              #'RSAPrivateKey'{version :: term(),
                                               modulus :: term(),
                                               publicExponent :: term(),
                                               privateExponent :: term(),
                                               prime1 :: term(),
                                               prime2 :: term(),
                                               exponent1 :: term(),
                                               exponent2 :: term(),
                                               coefficient :: term(),
                                               otherPrimeInfos :: term()},
                          MLDSA :: crypto:mldsa(),
                          MLDSAKeys ::
                              {#'ML-DSAPublicKey'{algorithm :: crypto:mldsa(), key :: binary()},
                               #'ML-DSAPrivateKey'{algorithm :: crypto:mldsa(),
                                                   seed :: binary(),
                                                   expandedkey :: binary()}},
                          SLHDSA :: crypto:slh_dsa(),
                          SLHDSAKeys ::
                              {#'SLH-DSAPublicKey'{algorithm :: crypto:slh_dsa(), key :: binary()},
                               #'SLH-DSAPrivateKey'{algorithm :: crypto:slh_dsa(), key :: binary()}}.
```

Generates a new key pair. Note that except for Diffie-Hellman the public key is
included in the private key structure. See also `crypto:generate_key/2`

# `decrypt_private`
*since OTP R14B* 

```erlang
-spec decrypt_private(CipherText, Key) -> PlainText
                         when CipherText :: binary(), Key :: rsa_private_key(), PlainText :: binary().
```

# `decrypt_private`
*since OTP R14B* 

```erlang
-spec decrypt_private(CipherText, Key, Options) -> PlainText
                         when
                             CipherText :: binary(),
                             Key :: rsa_private_key(),
                             Options :: crypto:pk_encrypt_decrypt_opts(),
                             PlainText :: binary().
```

Public-key decryption using the private key. See also `crypto:private_decrypt/4`

> #### Warning {: .warning }
>
> This is a legacy function, for security reasons do not use with rsa_pkcs1_padding.

# `decrypt_public`
*since OTP R14B* 

```erlang
-spec decrypt_public(CipherText, Key) -> PlainText
                        when CipherText :: binary(), Key :: rsa_public_key(), PlainText :: binary().
```

# `decrypt_public`
*since OTP R14B* 

```erlang
-spec decrypt_public(CipherText, Key, Options) -> PlainText
                        when
                            CipherText :: binary(),
                            Key :: rsa_public_key(),
                            Options :: crypto:pk_encrypt_decrypt_opts(),
                            PlainText :: binary().
```

Public-key decryption using the public key. See also `crypto:public_decrypt/4`

> #### Warning {: .warning }
>
> This is a legacy function, for security reasons do not use  with rsa_pkcs1_padding.
> For digital signatures the use of [`verify/4`](`verify/4`) together
> with [`sign/3`](`sign/3`) is a prefered solution.

# `encrypt_private`
*since OTP R14B* 

```erlang
-spec encrypt_private(PlainText, Key) -> CipherText
                         when PlainText :: binary(), Key :: rsa_private_key(), CipherText :: binary().
```

# `encrypt_private`
*since OTP 21.1* 

```erlang
-spec encrypt_private(PlainText, Key, Options) -> CipherText
                         when
                             PlainText :: binary(),
                             Key :: rsa_private_key(),
                             Options :: crypto:pk_encrypt_decrypt_opts() | custom_key_opts(),
                             CipherText :: binary().
```

Public-key encryption using the private key.

See also `crypto:private_encrypt/4`. The key can, besides a standard
RSA key, be a map specifing the key algorithm `rsa` and a fun to
handle the encryption operation.  This may be used for customized the
encryption operation with for instance hardware security modules (HSM)
or trusted platform modules (TPM).

> #### Warning {: .warning }
>
> This is a legacy function, for security reasons do not use with rsa_pkcs1_padding.
> For digital signatures use of [`sign/3`](`sign/3`) together with [`verify/4`](`verify/4`)  is
> the prefered solution.

# `encrypt_public`
*since OTP R14B* 

```erlang
-spec encrypt_public(PlainText, Key) -> CipherText
                        when PlainText :: binary(), Key :: rsa_public_key(), CipherText :: binary().
```

# `encrypt_public`
*since OTP 21.1* 

```erlang
-spec encrypt_public(PlainText, Key, Options) -> CipherText
                        when
                            PlainText :: binary(),
                            Key :: rsa_public_key(),
                            Options :: crypto:pk_encrypt_decrypt_opts(),
                            CipherText :: binary().
```

Public-key encryption using the public key. See also `crypto:public_encrypt/4`.

> #### Warning {: .warning }
>
> This is a legacy function, for security reasons do not use with rsa_pkcs1_padding.

# `pem_decode`
*since OTP R14B* 

```erlang
-spec pem_decode(binary()) -> [pem_entry()].
```

Decodes PEM binary data and returns entries as ASN.1 DER encoded entities.

Example
`{ok, PemBin} = file:read_file("cert.pem"). PemEntries = public_key:pem_decode(PemBin).`

# `pem_encode`
*since OTP R14B* 

```erlang
-spec pem_encode([pem_entry()]) -> binary().
```

Creates a PEM binary.

# `pem_entry_decode`
*since OTP R14B* 

```erlang
-spec pem_entry_decode(PemEntry) -> term() when PemEntry :: pem_entry().
```

# `pem_entry_decode`
*since OTP R14B* 

```erlang
-spec pem_entry_decode(PemEntry, Password) -> term()
                          when PemEntry :: pem_entry(), Password :: iodata() | fun(() -> iodata()).
```

Decodes a PEM entry. [`pem_decode/1`](`pem_decode/1`) returns a list of PEM
entries. Notice that if the PEM entry is of type 'SubjectPublickeyInfo', it is
further decoded to an `t:rsa_public_key/0` or `t:dsa_public_key/0`.

Password can be either an octet string or function which returns same type.

# `pem_entry_encode`
*since OTP R14B* 

```erlang
-spec pem_entry_encode(Asn1Type, Entity) -> pem_entry()
                          when Asn1Type :: pki_asn1_type(), Entity :: term().
```

# `pem_entry_encode`
*since OTP R14B* 

```erlang
-spec pem_entry_encode(Asn1Type, Entity, InfoPwd) -> pem_entry()
                          when
                              Asn1Type :: pki_asn1_type(),
                              Entity :: term(),
                              InfoPwd :: {CipherInfo, Password},
                              CipherInfo ::
                                  {Cipher :: iodata(),
                                   Salt ::
                                       binary() |
                                       {#'PBEParameter'{salt :: term(), iterationCount :: term()},
                                        digest_type()} |
                                       #'PBES2-params'{keyDerivationFunc :: term(),
                                                       encryptionScheme :: term()}},
                              Password :: iodata().
```

Creates a PEM entry that can be feed to [`pem_encode/1`](`pem_encode/1`).

If `Asn1Type` is `'SubjectPublicKeyInfo'`, `Entity` must be either an
`t:rsa_public_key/0`, `t:dsa_public_key/0` or an `t:ecdsa_public_key/0` and this
function creates the appropriate `'SubjectPublicKeyInfo'` entry.

# `pkix_sign`
*since OTP R14B* 

```erlang
-spec pkix_sign(Cert, Key) -> Der
                   when
                       Cert ::
                           #'OTPTBSCertificate'{version :: term(),
                                                serialNumber :: term(),
                                                signature :: term(),
                                                issuer :: term(),
                                                validity :: term(),
                                                subject :: term(),
                                                subjectPublicKeyInfo :: term(),
                                                issuerUniqueID :: term(),
                                                subjectUniqueID :: term(),
                                                extensions :: term()},
                       Key :: private_key(),
                       Der :: der_encoded().
```

Signs an 'OTPTBSCertificate'. Returns the corresponding DER-encoded certificate.

# `pkix_verify`
*since OTP R14B* 

```erlang
-spec pkix_verify(Cert, Key) -> boolean() when Cert :: der_encoded(), Key :: public_key().
```

Verifies PKIX x.509 certificate signature.

# `sign`

```erlang
-spec sign(Msg, DigestType, Key) -> Signature
              when
                  Msg :: binary() | {digest, binary()},
                  DigestType :: digest_type(),
                  Key :: private_key(),
                  Signature :: binary().
```

# `sign`
*since OTP 20.1* 

```erlang
-spec sign(Msg, DigestType, Key, Options) -> Signature
              when
                  Msg :: binary() | {digest, binary()},
                  DigestType :: digest_type(),
                  Key :: private_key(),
                  Options :: crypto:pk_sign_verify_opts() | custom_key_opts(),
                  Signature :: binary().
```

Creates a digital signature.

The `Msg` is either the binary "plain text" data to be signed or it is the
hashed value of "plain text", that is, the digest. The key can, besides a
standard key, be a map specifing a key algorithm and a fun that should handle
the signing. This may be used for customized signing with for instance hardware
security modules (HSM) or trusted platform modules (TPM).

# `verify`
*since OTP R14B* 

```erlang
-spec verify(Msg, DigestType, Signature, Key) -> boolean()
                when
                    Msg :: binary() | {digest, binary()},
                    DigestType :: digest_type(),
                    Signature :: binary(),
                    Key :: public_key().
```

# `verify`
*since OTP 20.1* 

```erlang
-spec verify(Msg, DigestType, Signature, Key, Options) -> boolean()
                when
                    Msg :: binary() | {digest, binary()},
                    DigestType :: digest_type(),
                    Signature :: binary(),
                    Key :: public_key(),
                    Options :: crypto:pk_sign_verify_opts().
```

Verifies a digital signature.

The `Msg` is either the binary "plain text" data or it is the hashed value of
"plain text", that is, the digest.

# `pkix_test_data`
*since OTP 20.1* 

```erlang
-spec pkix_test_data(ChainConf) -> TestConf
                        when
                            ChainConf ::
                                #{server_chain := chain_opts(), client_chain := chain_opts()} |
                                chain_opts(),
                            TestConf ::
                                #{server_config := [conf_opt()], client_config := [conf_opt()]} |
                                [conf_opt()].
```

Creates certificate configuration(s) consisting of certificate and its private
key plus CA certificate bundle, for a client and a server, intended to
facilitate automated testing of applications using X509-certificates, often
through SSL/TLS. The test data can be used when you have control over both the
client and the server in a test scenario.

When this function is called with a map containing client and server chain
specifications; it generates both a client and a server certificate chain where
the `cacerts` returned for the server contains the root cert the server should
trust and the intermediate certificates the server should present to connecting
clients. The root cert the server should trust is the one used as root of the
client certificate chain. Vice versa applies to the `cacerts` returned for the
client. The root cert(s) can either be pre-generated with
[pkix_test_root_cert/2 ](`pkix_test_root_cert/2`), or if options are specified;
it is (they are) generated.

When this function is called with a list of certificate options; it generates a
configuration with just one node certificate where `cacerts` contains the root
cert and the intermediate certs that should be presented to a peer. In this case
the same root cert must be used for all peers. This is useful in for example an
Erlang distributed cluster where any node, towards another node, acts either as
a server or as a client depending on who connects to whom. The generated
certificate contains a subject altname, which is not needed in a client
certificate, but makes the certificate useful for both roles.

Explanation of the options used to customize certificates in the generated
chains:

- **\{digest, digest_type()\}** - Hash algorithm to be used for signing the
  certificate together with the key option. Defaults to sha that is sha1.

- **\{key,  ec_params()| {rsa, Size:pos_integer(), Prime::pos_integer()} | private_key()\}** - Parameters to be used to call
  public_key:generate_key/1, to generate a key, or an existing key. Defaults to
  generating an ECDSA key. Note this could fail if Erlang/OTP is compiled with a
  very old cryptolib.

- **\{validity, \{From::erlang:timestamp(), To::erlang:timestamp()\}\}** - The
  validity period of the certificate.

- **\{extensions, \[#'Extension'\{\}]\}** - Extensions to include in the
  certificate.

  Default extensions included in CA certificates if not otherwise specified are:

  ```erlang
  [#'Extension'{extnID = ?'id-ce-keyUsage',
                extnValue = [keyCertSign, cRLSign],
                critical = false},
  #'Extension'{extnID = ?'id-ce-basicConstraints',
               extnValue = #'BasicConstraints'{cA = true},
               critical = true}]
  ```

  Default extensions included in the server peer cert if not otherwise specified
  are:

  ```erlang
  [#'Extension'{extnID = ?'id-ce-keyUsage',
                extnValue = [digitalSignature, keyAgreement],
                critical = false},
  #'Extension'{extnID = ?'id-ce-subjectAltName',
               extnValue = [{dNSName, Hostname}],
               critical = false}]
  ```

  Hostname is the result of calling net_adm:localhost() in the Erlang node where
  this function is called.

> #### Note {: .info }
>
> Note that the generated certificates and keys does not provide a formally
> correct PKIX-trust-chain and they cannot be used to achieve real security.
> This function is provided for testing purposes only.

# `pkix_test_root_cert`
*since OTP 20.2* 

```erlang
-spec pkix_test_root_cert(Name, Options) -> RootCertAndKey
                             when
                                 Name :: string(),
                                 Options :: [cert_opt()],
                                 RootCertAndKey :: #{cert := der_encoded(), key := private_key()}.
```

Generates a root certificate that can be used in multiple calls to
`pkix_test_data/1` when you want the same root certificate for several generated
certificates.

---

*Consult [api-reference.md](api-reference.md) for complete listing*
