crypto

Reference Manual

Version 4.2.1

- User's Guide
- Reference Manual
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### Table of Contents

- crypto (App)
- crypto
  - Top of manual page
  - block_decrypt/3
  - block_decrypt/4
  - block_decrypt/4
  - block_encrypt/3
  - block_encrypt/4
  - block_encrypt/4
  - block_encrypt/4
  - bytes_to_integer/1
  - cmac/3
  - cmac/4
  - compute_key/4
  - ec_curve/1
  - ec_curves/0
  - engine_ctrl_cmd_string/3
  - engine_ctrl_cmd_string/4
  - engine_get_all_methods/0
  - engine_list/0
  - engine_load/3
  - engine_load/4
  - engine_unload/1
  - exor/2
  - generate_key/2
  - generate_key/3
  - hash/2
  - hash_final/1
  - hash_init/1
  - hash_update/2
  - hmac/3
  - hmac/4
  - hmac_final/1
  - hmac_final_n/2
  - hmac_init/2
  - hmac_update/2
  - info_fips/0
  - info_lib/0
  - mod_pow/3
  - next_iv/2
  - next_iv/3
  - private_decrypt/4
  - private_encrypt/4
  - privkey_to_pubkey/2
  - public_decrypt/4
  - public_encrypt/4
  - rand_seed/1
  - rand_seed/0
  - rand_seed_s/0
  - rand_uniform/2
  - sign/4
  - sign/5
  - start/0
  - stop/0
  - stream_decrypt/2
  - stream_encrypt/2
  - stream_init/2
  - stream_init/3
  - strong_rand_bytes/1
  - supports/0
  - verify/5
  - verify/6

# crypto

### Module

crypto

### Module Summary

Crypto Functions

### Description

This module provides a set of cryptographic functions.

- Hash functions - Secure Hash Standard, The MD5 Message Digest Algorithm (RFC 1321) and The MD4 Message Digest Algorithm (RFC 1320)

- Hmac functions - Keyed-Hashing for Message Authentication (RFC 2104)

- Cmac functions - The AES-CMAC Algorithm (RFC 4493)

- Block ciphers - DES and AES in Block Cipher Modes - ECB, CBC, CFB, OFB, CTR and GCM

- RSA encryption RFC 1321

- Digital signatures Digital Signature Standard (DSS) and Elliptic Curve Digital Signature Algorithm (ECDSA)

- Secure Remote Password Protocol (SRP - RFC 2945)

- gcm: Dworkin, M., "Recommendation for Block Cipher Modes of Operation: Galois/Counter Mode (GCM) and GMAC", National Institute of Standards and Technology SP 800- 38D, November 2007.

### DATA TYPES

    key_value() = integer() | binary()

Always binary() when used as return value

    rsa_public() = [key_value()] = [E, N]

Where E is the public exponent and N is public modulus.

    rsa_private() = [key_value()] = [E, N, D] | [E, N, D, P1, P2, E1, E2, C]

Where E is the public exponent, N is public modulus and D is the private exponent. The longer key format contains redundant information that will make the calculation faster. P1,P2 are first and second prime factors. E1,E2 are first and second exponents. C is the CRT coefficient. Terminology is taken from RFC 3447.

    dss_public() = [key_value()] = [P, Q, G, Y]

Where P, Q and G are the dss parameters and Y is the public key.

    dss_private() = [key_value()] = [P, Q, G, X]

Where P, Q and G are the dss parameters and X is the private key.

    srp_public() = key_value()

Where is A or B from SRP design

    srp_private() = key_value()

Where is a or b from SRP design

Where Verifier is v, Generator is g and Prime is N, DerivedKey is X, and Scrambler is u (optional will be generated if not provided) from SRP design Version = '3' | '6' | '6a'

    dh_public() = key_value()

    dh_private() = key_value()

    dh_params() = [key_value()] = [P, G] | [P, G, PrivateKeyBitLength]

    ecdh_public() = key_value()

    ecdh_private() = key_value()

    ecdh_params() = ec_named_curve() | ec_explicit_curve()

    ec_explicit_curve() =
        {ec_field(), Prime :: key_value(), Point :: key_value(), Order :: integer(),
         CoFactor :: none | integer()}

    ec_field() = {prime_field, Prime :: integer()} |
        {characteristic_two_field, M :: integer(), Basis :: ec_basis()}

    ec_basis() = {tpbasis, K :: non_neg_integer()} |
        {ppbasis, K1 :: non_neg_integer(), K2 :: non_neg_integer(), K3 :: non_neg_integer()} |
        onbasis

    ec_named_curve() ->
          sect571r1| sect571k1| sect409r1| sect409k1| secp521r1| secp384r1| secp224r1| secp224k1|
          secp192k1| secp160r2| secp128r2| secp128r1| sect233r1| sect233k1| sect193r2| sect193r1|
          sect131r2| sect131r1| sect283r1| sect283k1| sect163r2| secp256k1| secp160k1| secp160r1|
          secp112r2| secp112r1| sect113r2| sect113r1| sect239k1| sect163r1| sect163k1| secp256r1|
          secp192r1|
          brainpoolP160r1| brainpoolP160t1| brainpoolP192r1| brainpoolP192t1| brainpoolP224r1|
          brainpoolP224t1| brainpoolP256r1| brainpoolP256t1| brainpoolP320r1| brainpoolP320t1|
          brainpoolP384r1| brainpoolP384t1| brainpoolP512r1| brainpoolP512t1

Note that the sect curves are GF2m (characteristic two) curves and are only supported if the underlying OpenSSL has support for them. See also crypto:supports/0

    engine_key_ref() = #{engine   := engine_ref(),
                                   key_id   := key_id(),
                                   password => password()}

    engine_ref() = term()

The result of a call to engine_load/3.

    key_id() = string() | binary()

Identifies the key to be used. The format depends on the loaded engine. It is passed to the ENGINE_load_(private|public)_key functions in libcrypto.

    password() = string() | binary()

The key's password

    stream_cipher() = rc4 | aes_ctr

    block_cipher() = aes_cbc | aes_cfb8 | aes_cfb128 | aes_ige256 | blowfish_cbc |
         blowfish_cfb64 | des_cbc | des_cfb | des3_cbc | des3_cfb | des_ede3 | rc2_cbc

    aead_cipher() = aes_gcm | chacha20_poly1305

    stream_key() = aes_key() | rc4_key()

    block_key() = aes_key() |  blowfish_key() | des_key()| des3_key()

    aes_key() = iodata()

Key length is 128, 192 or 256 bits

    rc4_key() = iodata()

Variable key length from 8 bits up to 2048 bits (usually between 40 and 256)

    blowfish_key() = iodata()

Variable key length from 32 bits up to 448 bits

    des_key() = iodata()

Key length is 64 bits (in CBC mode only 8 bits are used)

    des3_key() = [binary(), binary(), binary()]

Each key part is 64 bits (in CBC mode only 8 bits are used)

    digest_type() =  md5 | sha | sha224 | sha256 | sha384 | sha512

    rsa_digest_type() = md5 | ripemd160 | sha | sha224 | sha256 | sha384 | sha512

    dss_digest_type() = sha | sha224 | sha256 | sha384 | sha512

Note that the actual supported dss_digest_type depends on the underlying crypto library. In OpenSSL version >= 1.0.1 the listed digest are supported, while in 1.0.0 only sha, sha224 and sha256 are supported. In version 0.9.8 only sha is supported.

    ecdsa_digest_type() = sha | sha224 | sha256 | sha384 | sha512

    sign_options() = [{rsa_pad, rsa_sign_padding()} | {rsa_pss_saltlen, integer()}]

    rsa_sign_padding() = rsa_pkcs1_padding | rsa_pkcs1_pss_padding

     hash_algorithms() =  md5 | ripemd160 | sha | sha224 | sha256 | sha384 | sha512

md4 is also supported for hash_init/1 and hash/2. Note that both md4 and md5 are recommended only for compatibility with existing applications.

     cipher_algorithms() = aes_cbc | aes_cfb8 | aes_cfb128 | aes_ctr | aes_gcm |
         aes_ige256 | blowfish_cbc | blowfish_cfb64 | chacha20_poly1305 | des_cbc |
         des_cfb | des3_cbc | des3_cfb | des_ede3 | rc2_cbc | rc4

     mac_algorithms() = hmac | cmac

     public_key_algorithms() = rsa |dss | ecdsa | dh | ecdh | ec_gf2m

Note that ec_gf2m is not strictly a public key algorithm, but a restriction on what curves are supported with ecdsa and ecdh.

    engine_method_type() = engine_method_rsa | engine_method_dsa | engine_method_dh |
         engine_method_rand | engine_method_ecdh | engine_method_ecdsa |
         engine_method_ciphers | engine_method_digests | engine_method_store |
         engine_method_pkey_meths | engine_method_pkey_asn1_meths

### Exports

block_encrypt(Type, Key, PlainText) -> CipherText

### Types

Type = des_ecb | blowfish_ecb | aes_ecb
Key = block_key()
PlainText = iodata()

Encrypt PlainText according to Type block cipher.

May throw exception notsup in case the chosen Type is not supported by the underlying OpenSSL implementation.

block_decrypt(Type, Key, CipherText) -> PlainText

### Types

Type = des_ecb | blowfish_ecb | aes_ecb
Key = block_key()
PlainText = iodata()

Decrypt CipherText according to Type block cipher.

May throw exception notsup in case the chosen Type is not supported by the underlying OpenSSL implementation.

block_encrypt(Type, Key, Ivec, PlainText) -> CipherText
block_encrypt(AeadType, Key, Ivec, {AAD, PlainText}) -> {CipherText, CipherTag}
block_encrypt(aes_gcm, Key, Ivec, {AAD, PlainText, TagLength}) -> {CipherText, CipherTag}

### Types

Type = block_cipher()
AeadType = aead_cipher()
Key = block_key()
PlainText = iodata()
AAD = IVec = CipherText = CipherTag = binary()
TagLength = 1..16

Encrypt PlainText according to Type block cipher. IVec is an arbitrary initializing vector.

In AEAD (Authenticated Encryption with Associated Data) mode, encrypt PlainTextaccording to Type block cipher and calculate CipherTag that also authenticates the AAD (Associated Authenticated Data).

May throw exception notsup in case the chosen Type is not supported by the underlying OpenSSL implementation.

block_decrypt(Type, Key, Ivec, CipherText) -> PlainText
block_decrypt(AeadType, Key, Ivec, {AAD, CipherText, CipherTag}) -> PlainText | error

### Types

Type = block_cipher()
AeadType = aead_cipher()
Key = block_key()
PlainText = iodata()
AAD = IVec = CipherText = CipherTag = binary()

Decrypt CipherText according to Type block cipher. IVec is an arbitrary initializing vector.

In AEAD (Authenticated Encryption with Associated Data) mode, decrypt CipherTextaccording to Type block cipher and check the authenticity the PlainText and AAD (Associated Authenticated Data) using the CipherTag. May return error if the decryption or validation fail's

May throw exception notsup in case the chosen Type is not supported by the underlying OpenSSL implementation.

bytes_to_integer(Bin) -> Integer

### Types

Bin = binary() - as returned by crypto functions
Integer = integer()

Convert binary representation, of an integer, to an Erlang integer.

compute_key(Type, OthersPublicKey, MyKey, Params) -> SharedSecret

### Types

Type = dh | ecdh | srp
OthersPublicKey = dh_public() | ecdh_public() | srp_public()
MyKey = dh_private() | ecdh_private() | {srp_public(),srp_private()}
Params = dh_params() | ecdh_params() | SrpUserParams | SrpHostParams
SrpUserParams = {user, [DerivedKey::binary(), Prime::binary(), Generator::binary(), Version::atom() | [Scrambler:binary()]]}
SrpHostParams = {host, [Verifier::binary(), Prime::binary(), Version::atom() | [Scrambler::binary]]}
SharedSecret = binary()

Computes the shared secret from the private key and the other party's public key. See also public_key:compute_key/2

exor(Data1, Data2) -> Result

### Types

Data1, Data2 = iodata()
Result = binary()

Performs bit-wise XOR (exclusive or) on the data supplied.

generate_key(Type, Params) -> {PublicKey, PrivKeyOut}
generate_key(Type, Params, PrivKeyIn) -> {PublicKey, PrivKeyOut}

### Types

Type = dh | ecdh | rsa | srp
Params = dh_params() | ecdh_params() | RsaParams | SrpUserParams | SrpHostParams
RsaParams = {ModulusSizeInBits::integer(), PublicExponent::key_value()}
SrpUserParams = {user, [Generator::binary(), Prime::binary(), Version::atom()]}
SrpHostParams = {host, [Verifier::binary(), Generator::binary(), Prime::binary(), Version::atom()]}
PublicKey = dh_public() | ecdh_public() | rsa_public() | srp_public()
PrivKeyIn = undefined | dh_private() | ecdh_private() | srp_private()
PrivKeyOut = dh_private() | ecdh_private() | rsa_private() | srp_private()

Generates a public key of type Type. See also public_key:generate_key/1. May throw exception an exception of class error:

- badarg: an argument is of wrong type or has an illegal value,
- low_entropy: the random generator failed due to lack of secure "randomness",
- computation_failed: the computation fails of another reason than low_entropy.

Note

RSA key generation is only available if the runtime was built with dirty scheduler support. Otherwise, attempting to generate an RSA key will throw exception error:notsup.

hash(Type, Data) -> Digest

### Types

Type = md4 | hash_algorithms()
Data = iodata()
Digest = binary()

Computes a message digest of type Type from Data.

May throw exception notsup in case the chosen Type is not supported by the underlying OpenSSL implementation.

hash_init(Type) -> Context

### Types

Type = md4 | hash_algorithms()

Initializes the context for streaming hash operations. Type determines which digest to use. The returned context should be used as argument to hash_update.

May throw exception notsup in case the chosen Type is not supported by the underlying OpenSSL implementation.

hash_update(Context, Data) -> NewContext

### Types

Data = iodata()

Updates the digest represented by Context using the given Data. Context must have been generated using hash_init or a previous call to this function. Data can be any length. NewContext must be passed into the next call to hash_update or hash_final.

hash_final(Context) -> Digest

### Types

Digest = binary()

Finalizes the hash operation referenced by Context returned from a previous call to hash_update. The size of Digest is determined by the type of hash function used to generate it.

hmac(Type, Key, Data) -> Mac
hmac(Type, Key, Data, MacLength) -> Mac

### Types

Type = hash_algorithms() - except ripemd160
Key = iodata()
Data = iodata()
MacLength = integer()
Mac = binary()

Computes a HMAC of type Type from Data using Key as the authentication key.

MacLength will limit the size of the resultant Mac.

hmac_init(Type, Key) -> Context

### Types

Type = hash_algorithms() - except ripemd160
Key = iodata()
Context = binary()

Initializes the context for streaming HMAC operations. Type determines which hash function to use in the HMAC operation. Key is the authentication key. The key can be any length.

hmac_update(Context, Data) -> NewContext

### Types

Context = NewContext = binary()
Data = iodata()

Updates the HMAC represented by Context using the given Data. Context must have been generated using an HMAC init function (such as hmac_init). Data can be any length. NewContext must be passed into the next call to hmac_update or to one of the functions hmac_final and hmac_final_n

Warning

Do not use a Context as argument in more than one call to hmac_update or hmac_final. The semantics of reusing old contexts in any way is undefined and could even crash the VM in earlier releases. The reason for this limitation is a lack of support in the underlying OpenSSL API.

hmac_final(Context) -> Mac

### Types

Context = Mac = binary()

Finalizes the HMAC operation referenced by Context. The size of the resultant MAC is determined by the type of hash function used to generate it.

hmac_final_n(Context, HashLen) -> Mac

### Types

Context = Mac = binary()
HashLen = non_neg_integer()

Finalizes the HMAC operation referenced by Context. HashLen must be greater than zero. Mac will be a binary with at most HashLen bytes. Note that if HashLen is greater than the actual number of bytes returned from the underlying hash, the returned hash will have fewer than HashLen bytes.

cmac(Type, Key, Data) -> Mac
cmac(Type, Key, Data, MacLength) -> Mac

### Types

Type = block_cipher()
Key = iodata()
Data = iodata()
MacLength = integer()
Mac = binary()

Computes a CMAC of type Type from Data using Key as the authentication key.

MacLength will limit the size of the resultant Mac.

info_fips() -> Status

### Types

Status = enabled | not_enabled | not_supported

Provides information about the FIPS operating status of crypto and the underlying OpenSSL library. If crypto was built with FIPS support this can be either enabled (when running in FIPS mode) or not_enabled. For other builds this value is always not_supported.

Warning

In FIPS mode all non-FIPS compliant algorithms are disabled and throw exception not_supported. Check supports that in FIPS mode returns the restricted list of available algorithms.

info_lib() -> [{Name,VerNum,VerStr}]

### Types

Name = binary()
VerNum = integer()
VerStr = binary()

Provides the name and version of the libraries used by crypto.

Name is the name of the library. VerNum is the numeric version according to the library's own versioning scheme. VerStr contains a text variant of the version.

    > info_lib().
    [{<<"OpenSSL">>,269484095,<<"OpenSSL 1.1.0c  10 Nov 2016"">>}]

Note

From OTP R16 the numeric version represents the version of the OpenSSL header files (openssl/opensslv.h) used when crypto was compiled. The text variant represents the OpenSSL library used at runtime. In earlier OTP versions both numeric and text was taken from the library.

mod_pow(N, P, M) -> Result

### Types

N, P, M = binary() | integer()
Result = binary() | error

Computes the function N^P mod M.

next_iv(Type, Data) -> NextIVec
next_iv(Type, Data, IVec) -> NextIVec

### Types

Type = des_cbc | des3_cbc | aes_cbc | des_cfb
Data = iodata()
IVec = NextIVec = binary()

Returns the initialization vector to be used in the next iteration of encrypt/decrypt of type Type. Data is the encrypted data from the previous iteration step. The IVec argument is only needed for des_cfb as the vector used in the previous iteration step.

private_decrypt(Type, CipherText, PrivateKey, Padding) -> PlainText

### Types

Type = rsa
CipherText = binary()
PrivateKey = rsa_private() | engine_key_ref()
Padding = rsa_pkcs1_padding | rsa_pkcs1_oaep_padding | rsa_no_padding
PlainText = binary()

Decrypts the CipherText, encrypted with public_encrypt/4 (or equivalent function) using the PrivateKey, and returns the plaintext (message digest). This is a low level signature verification operation used for instance by older versions of the SSL protocol. See also public_key:decrypt_private/[2,3]

privkey_to_pubkey(Type, EnginePrivateKeyRef) -> PublicKey

### Types

Type = rsa | dss
EnginePrivateKeyRef = engine_key_ref()
PublicKey = rsa_public() | dss_public()

Fetches the corresponding public key from a private key stored in an Engine. The key must be of the type indicated by the Type parameter.

private_encrypt(Type, PlainText, PrivateKey, Padding) -> CipherText

### Types

Type = rsa
PlainText = binary()
The size of the PlainText must be less than byte_size(N)-11 if rsa_pkcs1_padding is used, and byte_size(N) if rsa_no_padding is used, where N is public modulus of the RSA key.
PrivateKey = rsa_private() | engine_key_ref()
Padding = rsa_pkcs1_padding | rsa_no_padding
CipherText = binary()

Encrypts the PlainText using the PrivateKey and returns the ciphertext. This is a low level signature operation used for instance by older versions of the SSL protocol. See also public_key:encrypt_private/[2,3]

public_decrypt(Type, CipherText, PublicKey, Padding) -> PlainText

### Types

Type = rsa
CipherText = binary()
PublicKey = rsa_public() | engine_key_ref()
Padding = rsa_pkcs1_padding | rsa_no_padding
PlainText = binary()

Decrypts the CipherText, encrypted with private_encrypt/4(or equivalent function) using the PrivateKey, and returns the plaintext (message digest). This is a low level signature verification operation used for instance by older versions of the SSL protocol. See also public_key:decrypt_public/[2,3]

public_encrypt(Type, PlainText, PublicKey, Padding) -> CipherText

### Types

Type = rsa
PlainText = binary()
The size of the PlainText must be less than byte_size(N)-11 if rsa_pkcs1_padding is used, and byte_size(N) if rsa_no_padding is used, where N is public modulus of the RSA key.
PublicKey = rsa_public() | engine_key_ref()
Padding = rsa_pkcs1_padding | rsa_pkcs1_oaep_padding | rsa_no_padding
CipherText = binary()

Encrypts the PlainText (message digest) using the PublicKey and returns the CipherText. This is a low level signature operation used for instance by older versions of the SSL protocol. See also public_key:encrypt_public/[2,3]

rand_seed(Seed) -> ok

### Types

Seed = binary()

Set the seed for PRNG to the given binary. This calls the RAND_seed function from openssl. Only use this if the system you are running on does not have enough "randomness" built in. Normally this is when strong_rand_bytes/1 throws low_entropy

rand_uniform(Lo, Hi) -> N

### Types

Lo, Hi, N = integer()

Generate a random number N, Lo =< N < Hi. Uses the crypto library pseudo-random number generator. Hi must be larger than Lo.

sign(Algorithm, DigestType, Msg, Key) -> binary()
sign(Algorithm, DigestType, Msg, Key, Options) -> binary()

### Types

Algorithm = rsa | dss | ecdsa
Msg = binary() | {digest,binary()}
The msg is either the binary "cleartext" data to be signed or it is the hashed value of "cleartext" i.e. the digest (plaintext).
DigestType = rsa_digest_type() | dss_digest_type() | ecdsa_digest_type()
Key = rsa_private() | dss_private() | [ecdh_private(),ecdh_params()] | engine_key_ref()
Options = sign_options()

Creates a digital signature.

Algorithm dss can only be used together with digest type sha.

See also public_key:sign/3.

start() -> ok

Equivalent to application:start(crypto).

stop() -> ok

Equivalent to application:stop(crypto).

strong_rand_bytes(N) -> binary()

### Types

N = integer()

Generates N bytes randomly uniform 0..255, and returns the result in a binary. Uses a cryptographically secure prng seeded and periodically mixed with operating system provided entropy. By default this is the RAND_bytes method from OpenSSL.

May throw exception low_entropy in case the random generator failed due to lack of secure "randomness".

rand_seed() -> rand:state()

Creates state object for random number generation, in order to generate cryptographically strong random numbers (based on OpenSSL's BN_rand_range), and saves it on process dictionary before returning it as well. See also rand:seed/1.

Example

    _ = crypto:rand_seed(),
    _IntegerValue = rand:uniform(42), % [1; 42]
    _FloatValue = rand:uniform().     % [0.0; 1.0[

rand_seed_s() -> rand:state()

Creates state object for random number generation, in order to generate cryptographically strongly random numbers (based on OpenSSL's BN_rand_range). See also rand:seed_s/1.

stream_init(Type, Key) -> State

### Types

Type = rc4
State = opaque()
Key = iodata()

Initializes the state for use in RC4 stream encryption stream_encrypt and stream_decrypt

stream_init(Type, Key, IVec) -> State

### Types

Type = aes_ctr
State = opaque()
Key = iodata()
IVec = binary()

Initializes the state for use in streaming AES encryption using Counter mode (CTR). Key is the AES key and must be either 128, 192, or 256 bits long. IVec is an arbitrary initializing vector of 128 bits (16 bytes). This state is for use with stream_encrypt and stream_decrypt.

stream_encrypt(State, PlainText) -> { NewState, CipherText}

### Types

Text = iodata()
CipherText = binary()

Encrypts PlainText according to the stream cipher Type specified in stream_init/3. Text can be any number of bytes. The initial State is created using stream_init. NewState must be passed into the next call to stream_encrypt.

stream_decrypt(State, CipherText) -> { NewState, PlainText }

### Types

CipherText = iodata()
PlainText = binary()

Decrypts CipherText according to the stream cipher Type specified in stream_init/3. PlainText can be any number of bytes. The initial State is created using stream_init. NewState must be passed into the next call to stream_decrypt.

supports() -> AlgorithmList

### Types

AlgorithmList = [{hashs, [hash_algorithms()]}, {ciphers, [cipher_algorithms()]}, {public_keys, [public_key_algorithms()]}, {macs, [mac_algorithms()]}]

Can be used to determine which crypto algorithms that are supported by the underlying OpenSSL library

ec_curves() -> EllipticCurveList

### Types

EllipticCurveList = [ec_named_curve()]

Can be used to determine which named elliptic curves are supported.

ec_curve(NamedCurve) -> EllipticCurve

### Types

NamedCurve = ec_named_curve()
EllipticCurve = ec_explicit_curve()

Return the defining parameters of a elliptic curve.

verify(Algorithm, DigestType, Msg, Signature, Key) -> boolean()
verify(Algorithm, DigestType, Msg, Signature, Key, Options) -> boolean()

### Types

Algorithm = rsa | dss | ecdsa
Msg = binary() | {digest,binary()}
The msg is either the binary "cleartext" data or it is the hashed value of "cleartext" i.e. the digest (plaintext).
DigestType = rsa_digest_type() | dss_digest_type() | ecdsa_digest_type()
Signature = binary()
Key = rsa_public() | dss_public() | [ecdh_public(),ecdh_params()] | engine_key_ref()
Options = sign_options()

Verifies a digital signature

Algorithm dss can only be used together with digest type sha.

See also public_key:verify/4.

engine_get_all_methods() -> Result

### Types

Result = [EngineMethod::atom()]

Returns a list of all possible engine methods.

May throw exception notsup in case there is no engine support in the underlying OpenSSL implementation.

See also the chapter Engine Load in the User's Guide.

engine_load(EngineId, PreCmds, PostCmds) -> Result

### Types

EngineId = unicode:chardata()
PreCmds, PostCmds = [{unicode:chardata(), unicode:chardata()}]
Result = {ok, Engine::term()} | {error, Reason::term()}

Loads the OpenSSL engine given by EngineId if it is available and then returns ok and an engine handle. This function is the same as calling engine_load/4 with EngineMethods set to a list of all the possible methods. An error tuple is returned if the engine can't be loaded.

The function throws a badarg if the parameters are in wrong format. It may also throw the exception notsup in case there is no engine support in the underlying OpenSSL implementation.

See also the chapter Engine Load in the User's Guide.

engine_load(EngineId, PreCmds, PostCmds, EngineMethods) -> Result

### Types

EngineId = unicode:chardata()
PreCmds, PostCmds = [{unicode:chardata(), unicode:chardata()}]
EngineMethods = [engine_method_type()]
Result = {ok, Engine::term()} | {error, Reason::term()}

Loads the OpenSSL engine given by EngineId if it is available and then returns ok and an engine handle. An error tuple is returned if the engine can't be loaded.

The function throws a badarg if the parameters are in wrong format. It may also throw the exception notsup in case there is no engine support in the underlying OpenSSL implementation.

See also the chapter Engine Load in the User's Guide.

engine_unload(Engine) -> Result

### Types

Engine = term()
Result = ok | {error, Reason::term()}

Unloads the OpenSSL engine given by EngineId. An error tuple is returned if the engine can't be unloaded.

The function throws a badarg if the parameter is in wrong format. It may also throw the exception notsup in case there is no engine support in the underlying OpenSSL implementation.

See also the chapter Engine Load in the User's Guide.

engine_list() -> Result

### Types

Result = [EngineId::unicode:chardata()]

List the id's of all engines in OpenSSL's internal list.

It may also throw the exception notsup in case there is no engine support in the underlying OpenSSL implementation.

See also the chapter Engine Load in the User's Guide.

engine_ctrl_cmd_string(Engine, CmdName, CmdArg) -> Result

### Types

Engine = term()
CmdName = unicode:chardata()
CmdArg = unicode:chardata()
Result = ok | {error, Reason::term()}

Sends ctrl commands to the OpenSSL engine given by Engine. This function is the same as calling engine_ctrl_cmd_string/4 with Optional set to false.

The function throws a badarg if the parameters are in wrong format. It may also throw the exception notsup in case there is no engine support in the underlying OpenSSL implementation.

engine_ctrl_cmd_string(Engine, CmdName, CmdArg, Optional) -> Result

### Types

Engine = term()
CmdName = unicode:chardata()
CmdArg = unicode:chardata()
Optional = boolean()
Result = ok | {error, Reason::term()}

Sends ctrl commands to the OpenSSL engine given by Engine. Optional is a boolean argument that can relax the semantics of the function. If set to true it will only return failure if the ENGINE supported the given command name but failed while executing it, if the ENGINE doesn't support the command name it will simply return success without doing anything. In this case we assume the user is only supplying commands specific to the given ENGINE so we set this to false.

The function throws a badarg if the parameters are in wrong format. It may also throw the exception notsup in case there is no engine support in the underlying OpenSSL implementation.