# crypto

### Module

### Module Summary

### Description

This module provides a set of cryptographic functions.

**Hash functions****MACs - Message Authentication Codes**-
**Hmac functions**- Keyed-Hashing for Message Authentication [RFC 2104]
**Cmac functions**- The AES-CMAC Algorithm [RFC 4493]
**POLY1305**- ChaCha20 and Poly1305 for IETF Protocols [RFC 7539]

**Symmetric Ciphers**-
**DES, 3DES and AES**- Block Cipher Techniques [NIST]
**Blowfish**- Fast Software Encryption, Cambridge Security Workshop Proceedings (December 1993), Springer-Verlag, 1994, pp. 191-204.
**Chacha20**- ChaCha20 and Poly1305 for IETF Protocols [RFC 7539]
**Chacha20_poly1305**- ChaCha20 and Poly1305 for IETF Protocols [RFC 7539]

**Modes**-
**ECB, CBC, CFB, OFB and CTR**- Recommendation for Block Cipher Modes of Operation: Methods and Techniques [NIST SP 800-38A]
**GCM**- Recommendation for Block Cipher Modes of Operation: Galois/Counter Mode (GCM) and GMAC [NIST SP 800-38D]
**CCM**- Recommendation for Block Cipher Modes of Operation: The CCM Mode for Authentication and Confidentiality [NIST SP 800-38C]

**Asymetric Ciphers - Public Key Techniques**

The actual supported algorithms and features depends on their availability in the actual libcrypto used. See the crypto (App) about dependencies.

Enabling FIPS mode will also disable algorithms and features.

The CRYPTO User's Guide has more information on FIPS, Engines and Algorithm Details like key lengths.

### Data Types

#### Ciphers

Stream ciphers for stream_encrypt/2 and stream_decrypt/2 .

cbc_cipher() |

cfb_cipher() |

aes_cbc128 |

aes_cbc256 |

aes_ige256 |

blowfish_ofb64 |

des3_cbf |

des_ede3 |

rc2_cbc

cbc_cipher() = des_cbc | des3_cbc | aes_cbc | blowfish_cbc

cfb_cipher() =

aes_cfb128 | aes_cfb8 | blowfish_cfb64 | des3_cfb | des_cfb

Block ciphers with initialization vector for block_encrypt/4 and block_decrypt/4 .

Block ciphers without initialization vector for block_encrypt/3 and block_decrypt/3 .

Ciphers with simultaneous MAC-calculation or MAC-checking. block_encrypt/4 and block_decrypt/4 .

#### Digests

sha2() = sha224 | sha256 | sha384 | sha512

sha3() = sha3_224 | sha3_256 | sha3_384 | sha3_512

The compatibility_only_hash() algorithms are recommended only for compatibility with existing applications.

#### Elliptic Curves

brainpoolP160r1 |

brainpoolP160t1 |

brainpoolP192r1 |

brainpoolP192t1 |

brainpoolP224r1 |

brainpoolP224t1 |

brainpoolP256r1 |

brainpoolP256t1 |

brainpoolP320r1 |

brainpoolP320t1 |

brainpoolP384r1 |

brainpoolP384t1 |

brainpoolP512r1 |

brainpoolP512t1 |

c2pnb163v1 |

c2pnb163v2 |

c2pnb163v3 |

c2pnb176v1 |

c2pnb208w1 |

c2pnb272w1 |

c2pnb304w1 |

c2pnb368w1 |

c2tnb191v1 |

c2tnb191v2 |

c2tnb191v3 |

c2tnb239v1 |

c2tnb239v2 |

c2tnb239v3 |

c2tnb359v1 |

c2tnb431r1 |

ipsec3 |

ipsec4 |

prime192v1 |

prime192v2 |

prime192v3 |

prime239v1 |

prime239v2 |

prime239v3 |

prime256v1 |

secp112r1 |

secp112r2 |

secp128r1 |

secp128r2 |

secp160k1 |

secp160r1 |

secp160r2 |

secp192k1 |

secp192r1 |

secp224k1 |

secp224r1 |

secp256k1 |

secp256r1 |

secp384r1 |

secp521r1 |

sect113r1 |

sect113r2 |

sect131r1 |

sect131r2 |

sect163k1 |

sect163r1 |

sect163r2 |

sect193r1 |

sect193r2 |

sect233k1 |

sect233r1 |

sect239k1 |

sect283k1 |

sect283r1 |

sect409k1 |

sect409r1 |

sect571k1 |

sect571r1 |

wtls1 |

wtls10 |

wtls11 |

wtls12 |

wtls3 |

wtls4 |

wtls5 |

wtls6 |

wtls7 |

wtls8 |

wtls9

edwards_curve_dh() = x25519 | x448

edwards_curve_ed() = ed25519 | ed448

Note that some curves are disabled if FIPS is enabled.

{Field :: ec_field(),

Curve :: ec_curve(),

BasePoint :: binary(),

Order :: binary(),

CoFactor :: none | binary()}

ec_field() = ec_prime_field() | ec_characteristic_two_field()

ec_curve() =

{A :: binary(), B :: binary(), Seed :: none | binary()}

Parametric curve definition.

ec_characteristic_two_field() =

{characteristic_two_field,

M :: integer(),

Basis :: ec_basis()}

ec_basis() =

{tpbasis, K :: integer() >= 0} |

{ppbasis,

K1 :: integer() >= 0,

K2 :: integer() >= 0,

K3 :: integer() >= 0} |

onbasis

Curve definition details.

#### Keys

For keylengths, iv-sizes and blocksizes see the User's Guide.

A key for des3 is a list of three iolists

Always binary() when used as return value

#### Public/Private Keys

rsa_private() = [key_integer()]

rsa_params() =

{ModulusSizeInBits :: integer(),

PublicExponent :: key_integer()}

rsa_public() = [E, N]

rsa_private() = [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() = [P, Q, G, Y]

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

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

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

ecdsa_private() = key_integer()

ecdsa_params() = ec_named_curve() | ec_explicit_curve()

srp_public() = key_integer()

Where is A or B from SRP design

srp_private() = key_integer()

Where is a or b from SRP design

{user, srp_user_gen_params()} | {host, srp_host_gen_params()}

srp_comp_params() =

{user, srp_user_comp_params()} |

{host, srp_host_comp_params()}

srp_user_gen_params() = [DerivedKey::binary(), Prime::binary(), Generator::binary(), Version::atom()]

srp_host_gen_params() = [Verifier::binary(), Prime::binary(), Version::atom() ]

srp_user_comp_params() = [DerivedKey::binary(), Prime::binary(), Generator::binary(), Version::atom() | ScramblerArg::list()]

srp_host_comp_params() = [Verifier::binary(), Prime::binary(), Version::atom() | ScramblerArg::list()]

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'

#### Public Key Ciphers

Algorithms for public key encrypt/decrypt. Only RSA is supported.

rsa_opt() =

{rsa_padding, rsa_padding()} |

{signature_md, atom()} |

{rsa_mgf1_md, sha} |

{rsa_oaep_label, binary()} |

{rsa_oaep_md, sha}

rsa_padding() =

rsa_pkcs1_padding |

rsa_pkcs1_oaep_padding |

rsa_sslv23_padding |

rsa_x931_padding |

rsa_no_padding

Options for public key encrypt/decrypt. Only RSA is supported.

The RSA options are experimental.

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

Those option forms are kept only for compatibility and should not be used in new code.

#### Public Key Sign and Verify

Algorithms for sign and verify.

rsa_sign_verify_opt() =

{rsa_padding, rsa_sign_verify_padding()} |

{rsa_pss_saltlen, integer()}

rsa_sign_verify_padding() =

rsa_pkcs1_padding |

rsa_pkcs1_pss_padding |

rsa_x931_padding |

rsa_no_padding

Options for sign and verify.

The RSA options are experimental.

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

#### Diffie-Hellman Keys and parameters

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

ecdh_private() = key_integer()

ecdh_params() =

ec_named_curve() | edwards_curve_dh() | ec_explicit_curve()

#### Types for Engines

#{engine := engine_ref(),

key_id := key_id(),

password => password(),

term() => term()}

engine_ref() = term()

The result of a call to engine_load/3.

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.

The password of the key stored in an engine.

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 |

engine_method_ec

Pre and Post commands for engine_load/3 and /4.

#### Internal data types

Contexts with an internal state that should not be manipulated but passed between function calls.

### Exports

Encrypt PlainText according to Type block cipher.

May raise exception error:notsup in case the chosen Type is not supported by the underlying libcrypto implementation.

For keylengths and blocksizes see the User's Guide.

Decrypt CipherText according to Type block cipher.

May raise exception error:notsup in case the chosen Type is not supported by the underlying libcrypto implementation.

For keylengths and blocksizes see the User's Guide.

### Types

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 raise exception error:notsup in case the chosen Type is not supported by the underlying libcrypto implementation.

For keylengths, iv-sizes and blocksizes see the User's Guide.

### Types

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

For keylengths, iv-sizes and blocksizes see the User's Guide.

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

### Types

dh_private() | ecdh_private() | {srp_public(), srp_private()}

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

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

### Types

dh_public() | ecdh_public() | rsa_public() | srp_public()

undefined |

dh_private() |

ecdh_private() |

rsa_private() |

{srp_public(), srp_private()}

dh_private() |

ecdh_private() |

rsa_private() |

{srp_public(), srp_private()}

dh_params() | ecdh_params() | rsa_params() | srp_comp_params()

Generates a public key of type Type. See also public_key:generate_key/1. May raise exception:

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

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

### Types

sha1() |

sha2() |

sha3() |

ripemd160 |

compatibility_only_hash()

Computes a message digest of type Type from Data.

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

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.

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.

### Types

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

MacLength will limit the size of the resultant Mac.

### Types

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.

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

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 libcrypto API.

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.

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.

### Types

cbc_cipher() |

cfb_cipher() |

blowfish_cbc |

des_ede3 |

rc2_cbc

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

MacLength will limit the size of the resultant Mac.

Provides information about the FIPS operating status of crypto and the underlying libcrypto 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.

See enable_fips_mode/1 about how to enable FIPS mode.

In FIPS mode all non-FIPS compliant algorithms are disabled and raise exception error:notsup. Check supports that in FIPS mode returns the restricted list of available algorithms.

### Types

Enables (Enable = true) or disables (Enable = false) FIPS mode. Returns true if the operation was successful or false otherwise.

Note that to enable FIPS mode succesfully, OTP must be built with the configure option --enable-fips, and the underlying libcrypto must also support FIPS.

See also info_fips/0.

### Types

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"">>}]
```

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 libcrypto library used at runtime.
In earlier OTP versions both numeric and text was taken from the library.

### Types

Computes the function N^P mod M.

### Types

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.

### Types

Computes a POLY1305 message authentication code (Mac) from Data using Key as the authentication key.

### Types

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]

### Types

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]

### Types

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]

### Types

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]

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 raises error:low_entropy

### Types

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

Equivalent to application:start(crypto).

Equivalent to application:stop(crypto).

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 raise exception error:low_entropy in case the random generator failed due to lack of secure "randomness".

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 in the process dictionary before returning it as well. See also rand:seed/1 and rand_seed_s/0.

When using the state object from this function the rand functions using it may raise exception error:low_entropy in case the random generator failed due to lack of secure "randomness".

**Example**

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

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.

When using the state object from this function the rand functions using it may raise exception error:low_entropy in case the random generator failed due to lack of secure "randomness".

The state returned from this function can not be used to get a reproducable random sequence as from the other rand functions, since reproducability does not match cryptographically safe.

The only supported usage is to generate one distinct random sequence from this start state.

### Types

Creates state object for random number generation, in order to generate cryptographically strong random numbers. See also rand:seed/1 and rand_seed_alg_s/1.

When using the state object from this function the rand functions using it may raise exception error:low_entropy in case the random generator failed due to lack of secure "randomness".

The cache size can be changed from its default value using the crypto app's configuration parameter rand_cache_size.

**Example**

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

### Types

Creates state object for random number generation, in order to generate cryptographically strongly random numbers. See also rand:seed_s/1.

If Alg is crypto this function behaves exactly like rand_seed_s/0.

If Alg is crypto_cache this function fetches random data with OpenSSL's RAND_bytes and caches it for speed using an internal word size of 56 bits that makes calculations fast on 64 bit machines.

The cache size can be changed from its default value using the crypto app's configuration parameter rand_cache_size.

The state returned from this function can not be used to get a reproducable random sequence as from the other rand functions, since reproducability does not match cryptographically safe.

In fact since random data is cached some numbers may get reproduced if you try, but this is unpredictable.

The only supported usage is to generate one distinct random sequence from this start state.

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

For keylengths see the User's Guide.

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.

For keylengths and iv-sizes see the User's Guide.

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.

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.

### Types

{hashs, Hashs} |

{ciphers, Ciphers} |

{public_keys, PKs} |

{macs, Macs} |

{curves, Curves} |

{rsa_opts, RSAopts}

[sha1() |

sha2() |

sha3() |

ripemd160 |

compatibility_only_hash()]

[stream_cipher() |

block_cipher_with_iv() |

block_cipher_without_iv() |

aead_cipher()]

[ec_named_curve() | edwards_curve_dh() | edwards_curve_ed()]

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

Note: the rsa_opts entry is in an experimental state and may change or be removed without notice. No guarantee for the accuarcy of the rsa option's value list should be assumed.

### Types

ec_named_curve() | edwards_curve_dh() | edwards_curve_ed()

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

Return the defining parameters of a elliptic curve.

### Types

rsa_digest_type() |

dss_digest_type() |

ecdsa_digest_type() |

none

rsa_private() |

dss_private() |

[ecdsa_private() | ecdsa_params()] |

[eddsa_private() | eddsa_params()] |

engine_key_ref()

Creates a digital signature.

The msg is either the binary "cleartext" data to be signed or it is the hashed value of "cleartext" i.e. the digest (plaintext).

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

See also public_key:sign/3.

### Types

rsa_digest_type() | dss_digest_type() | ecdsa_digest_type()

rsa_public() |

dss_public() |

[ecdsa_public() | ecdsa_params()] |

[eddsa_public() | eddsa_params()] |

engine_key_ref()

Verifies a digital signature

The msg is either the binary "cleartext" data to be signed or it is the hashed value of "cleartext" i.e. the digest (plaintext).

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

See also public_key:verify/4.

### Types

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.

### Types

Returns a list of all possible engine methods.

May raise exception error:notsup in case there is no engine support in the underlying OpenSSL implementation.

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

### Types

{ok, Engine :: engine_ref()} | {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 raises a error:badarg if the parameters are in wrong format. It may also raise the exception error:notsup in case there is no engine support in the underlying OpenSSL implementation.

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

### Types

{ok, Engine :: engine_ref()} | {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 raises a error:badarg if the parameters are in wrong format. It may also raise the exception error:notsup in case there is no engine support in the underlying OpenSSL implementation.

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

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

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

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

### Types

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

Get a reference to an already loaded engine with EngineId. An error tuple is returned if the engine can't be unloaded.

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

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

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 raises a error:badarg if the parameters are in wrong format. It may also raise the exception error:notsup in case there is no engine support in the underlying OpenSSL implementation.

### Types

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.

Add the engine to OpenSSL's internal list.

Remove the engine from OpenSSL's internal list.

Return the ID for the engine, or an empty binary if there is no id set.

Return the name (eg a description) for the engine, or an empty binary if there is no name set.

### Types

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

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

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

May raise exception error:notsup in case engine functionality is not supported by the underlying OpenSSL implementation.

### Types

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

Loads the OpenSSL engine given by EngineId and the path to the dynamic library implementing the engine. This function is the same as calling ensure_engine_loaded/3 with EngineMethods set to a list of all the possible methods. An error tuple is returned if the engine can't be loaded.

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

### Types

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

Loads the OpenSSL engine given by EngineId and the path to the dynamic library implementing the engine. This function differs from the normal engine_load in that sense it also add the engine id to the internal list in OpenSSL. Then in the following calls to the function it just fetch the reference to the engine instead of loading it again. An error tuple is returned if the engine can't be loaded.

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

Unloads an engine loaded with the ensure_engine_loaded function. It both removes the label from the OpenSSL internal engine list and unloads the engine. This function is the same as calling ensure_engine_unloaded/2 with EngineMethods set to a list of all the possible methods. An error tuple is returned if the engine can't be unloaded.

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

### Types

Unloads an engine loaded with the ensure_engine_loaded function. It both removes the label from the OpenSSL internal engine list and unloads the engine. An error tuple is returned if the engine can't be unloaded.

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