# 5 Algorithm Details

This chapter describes details of algorithms in the crypto application.

The tables only documents the supported cryptos and key lengths. The user should not draw any conclusion on security from the supplied tables.

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5.1 Ciphers

A cipher in the new api is categorized as either cipher_no_iv(), cipher_iv() or cipher_aead(). The letters IV are short for Initialization Vector and AEAD is an abbreviation of Authenticated Encryption with Associated Data.

Due to irregular naming conventions, some cipher names in the old api are substituted by new names in the new api. For a list of retired names, see Retired cipher names.

To dynamically check availability, check that the name in the Cipher and Mode column is present in the list returned by crypto:supports(ciphers).

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Ciphers without an IV - cipher_no_iv()

To be used with:

- crypto_one_time/4
- crypto_init/3

The ciphers are:

Cipher and Mode | Key length [bytes] | Block size [bytes]
aes_128_ecb | 16 | 16
aes_192_ecb | 24 | 16
aes_256_ecb | 32 | 16
blowfish_ecb | 16 | 8
des_ecb | 8 | 8
rc4 | 16 | 1

Table 5.1: Ciphers without IV

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Ciphers with an IV - cipher_iv()

To be used with:

- crypto_one_time/5
- crypto_init/4
- crypto_dyn_iv_init/3

The ciphers are:

Cipher and Mode | Key length [bytes] | IV length [bytes] | Block size [bytes] | Limited to OpenSSL versions
aes_128_cbc | 16 | 16 | 16 |
aes_192_cbc | 24 | 16 | 16 |
aes_256_cbc | 32 | 16 | 16 |
aes_128_cfb8 | 16 | 16 | 1 |
aes_192_cfb8 | 24 | 16 | 1 |
aes_256_cfb8 | 32 | 16 | 1 |
aes_128_cfb128 | 16 | 16 | 1 |
aes_192_cfb128 | 24 | 16 | 1 |
aes_256_cfb128 | 32 | 16 | 1 |
aes_128_ctr | 16 | 16 | 1 |
aes_192_ctr | 24 | 16 | 1 |
aes_256_ctr | 32 | 16 | 1 |
aes_128_ofb | 16 | 16 | 1 |
aes_192_ofb | 24 | 16 | 1 |
aes_256_ofb | 32 | 16 | 1 |
blowfish_cbc | 16 | 8 | 8 |
blowfish_cfb64 | 16 | 8 | 1 |
blowfish_ofb64 | 16 | 8 | 1 |
chacha20 | 32 | 16 | 1 | ≥1.1.0d
des_cbc | 8 | 8 | 8 |
des_ede3_cbc | 24 | 8 | 8 |
des_cfb | 8 | 8 | 1 |
des_ede3_cfb | 24 | 8 | 1 |
rc2_cbc | 16 | 8 | 8 |

Table 5.2: Ciphers with IV

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Ciphers with AEAD - cipher_aead()

To be used with:

- crypto_one_time_aead/6
- crypto_one_time_aead/7

The ciphers are:

Cipher and Mode | Key length [bytes] | IV length [bytes] | AAD length [bytes] | Tag length [bytes] | Block size [bytes] | Limited to OpenSSL versions
aes_128_ccm | 16 | 7-13 | any | even 4-16 default: 12 | any | ≥1.0.1
aes_192_ccm | 24 | 7-13 | any | even 4-16 default: 12 | any | ≥1.0.1
aes_256_ccm | 32 | 7-13 | any | even 4-16 default: 12 | any | ≥1.0.1
aes_128_gcm | 16 | ≥1 | any | 1-16 default: 16 | any | ≥1.0.1
aes_192_gcm | 24 | ≥1 | any | 1-16 default: 16 | any | ≥1.0.1
aes_256_gcm | 32 | ≥1 | any | 1-16 default: 16 | any | ≥1.0.1
chacha20_poly1305 | 32 | 1-16 | any | 16 | any | ≥1.1.0

Table 5.3: AEAD ciphers

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5.2 Message Authentication Codes (MACs)

To be used in mac/4 and related functions.

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CMAC

CMAC with the following ciphers are available with OpenSSL 1.0.1 or later if not disabled by configuration.

To dynamically check availability, check that the name cmac is present in the list returned by crypto:supports(macs). Also check that the name in the Cipher and Mode column is present in the list returned by crypto:supports(ciphers).

Cipher and Mode | Key length [bytes] | Max Mac Length (= default length) [bytes]
aes_128_cbc | 16 | 16
aes_192_cbc | 24 | 16
aes_256_cbc | 32 | 16
aes_128_ecb | 16 | 16
aes_192_ecb | 24 | 16
aes_256_ecb | 32 | 16
blowfish_cbc | 16 | 8
blowfish_ecb | 16 | 8
des_cbc | 8 | 8
des_ecb | 8 | 8
des_ede3_cbc | 24 | 8
rc2_cbc | 16 | 8

Table 5.4: CMAC cipher key lengths

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HMAC

Available in all OpenSSL compatible with Erlang CRYPTO if not disabled by configuration.

To dynamically check availability, check that the name hmac is present in the list returned by crypto:supports(macs) and that the hash name is present in the list returned by crypto:supports(hashs).

Hash | Max Mac Length (= default length) [bytes]
sha | 20
sha224 | 28
sha256 | 32
sha384 | 48
sha512 | 64
sha3_224 | 28
sha3_256 | 32
sha3_384 | 48
sha3_512 | 64
shake128 | 64
shake256 | 64
blake2b | 64
blake2s | 32
md4 | 16
md5 | 16
ripemd160 | 20

Table 5.5: HMAC output sizes

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POLY1305

POLY1305 is available with OpenSSL 1.1.1 or later if not disabled by configuration.

To dynamically check availability, check that the name poly1305 is present in the list returned by crypto:supports(macs).

The poly1305 mac wants an 32 bytes key and produces a 16 byte MAC by default.

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5.3 Hash

To dynamically check availability, check that the wanted name in the Names column is present in the list returned by crypto:supports(hashs).

Type | Names | Limited to OpenSSL versions
SHA1 | sha |
SHA2 | sha224, sha256, sha384, sha512 |
SHA3 | sha3_224, sha3_256, sha3_384, sha3_512, shake128, shake256 | ≥1.1.1
MD4 | md4 |
MD5 | md5 |
RIPEMD | ripemd160 |

Table 5.6:

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5.4 Public Key Cryptography

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RSA

RSA is available with all OpenSSL versions compatible with Erlang CRYPTO if not disabled by configuration. To dynamically check availability, check that the atom rsa is present in the list returned by crypto:supports(public_keys).

Warning

The RSA options are experimental.

The exact set of options and there syntax may be changed without prior notice.

Option | sign/verify | public encrypt private decrypt | private encrypt public decrypt
{rsa_padding,rsa_x931_padding} | x |  | x
{rsa_padding,rsa_pkcs1_padding} | x | x | x
{rsa_padding,rsa_pkcs1_pss_padding} {rsa_pss_saltlen, -2..} {rsa_mgf1_md, atom()} | x (2) x (2) x (2) |  |
{rsa_padding,rsa_pkcs1_oaep_padding} {rsa_mgf1_md, atom()} {rsa_oaep_label, binary()}} {rsa_oaep_md, atom()} |  | x (2) x (2) x (3) x (3) |
{rsa_padding,rsa_no_padding} | x (1) |  |

Table 5.7:

Notes:

1. (1) OpenSSL ≤ 1.0.0
2. (2) OpenSSL ≥ 1.0.1
3. (3) OpenSSL ≥ 1.1.0

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DSS

DSS is available with OpenSSL versions compatible with Erlang CRYPTO if not disabled by configuration. To dynamically check availability, check that the atom dss is present in the list returned by crypto:supports(public_keys).

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ECDSA

ECDSA is available with OpenSSL 0.9.8o or later if not disabled by configuration. To dynamically check availability, check that the atom ecdsa is present in the list returned by crypto:supports(public_keys). If the atom ec_gf2m also is present, the characteristic two field curves are available.

The actual supported named curves could be checked by examining the list returned by crypto:supports(curves).

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EdDSA

EdDSA is available with OpenSSL 1.1.1 or later if not disabled by configuration. To dynamically check availability, check that the atom eddsa is present in the list returned by crypto:supports(public_keys).

Support for the curves ed25519 and ed448 is implemented. The actual supported named curves could be checked by examining the list with the list returned by crypto:supports(curves).

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Diffie-Hellman

Diffie-Hellman computations are available with OpenSSL versions compatible with Erlang CRYPTO if not disabled by configuration. To dynamically check availability, check that the atom dh is present in the list returned by crypto:supports(public_keys).

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Elliptic Curve Diffie-Hellman

Elliptic Curve Diffie-Hellman is available with OpenSSL 0.9.8o or later if not disabled by configuration. To dynamically check availability, check that the atom ecdh is present in the list returned by crypto:supports(public_keys).

The Edward curves x25519 and x448 are supported with OpenSSL 1.1.1 or later if not disabled by configuration.

The actual supported named curves could be checked by examining the list returned by crypto:supports(curves).