`evp`

—

high level cryptographic functions

```
#include
<openssl/evp.h>
```

The EVP library provides a high level interface to cryptographic functions.

EVP_SealInit(3) and

EVP_OpenInit(3) provide
public key encryption and decryption to implement digital
"envelopes".

The

EVP_DigestSignInit(3)
and

EVP_DigestVerifyInit(3)
functions implement digital signatures and Message Authentication Codes
(MACs). Also see the older

EVP_SignInit(3) and

EVP_VerifyInit(3)
functions.

Symmetric encryption is available with the

EVP_EncryptInit(3)
functions. The

EVP_DigestInit(3)
functions provide message digests.

Authenticated encryption with additional data (AEAD) is available with the

EVP_AEAD_CTX_init(3)
functions.

The

`EVP_PKEY_*`

() functions provide a high
level interface to asymmetric algorithms. To create a new

`EVP_PKEY`, see

EVP_PKEY_new(3).

`EVP_PKEY`s can be associated with a private
key of a particular algorithm by using the functions described in the

EVP_PKEY_set1_RSA(3)
page, or new keys can be generated using

EVP_PKEY_keygen(3).

`EVP_PKEY`s can be compared using

EVP_PKEY_cmp(3) or printed
using

EVP_PKEY_print_private(3).

The

`EVP_PKEY_*`

() functions support the full
range of asymmetric algorithm operations:

The

EVP_BytesToKey(3)
function provides some limited support for password based encryption. Careful
selection of the parameters will provide a PKCS#5 PBKDF1 compatible
implementation. However, new applications should typically not use this
(preferring, for example, PBKDF2 from PCKS#5).

Algorithms are loaded with

OpenSSL_add_all_algorithms(3).

All the symmetric algorithms (ciphers), digests and asymmetric algorithms
(public key algorithms) can be replaced by

`ENGINE` modules providing alternative
implementations; see

ENGINE_register_RSA(3)
and the related manual pages for more information. If

`ENGINE` implementations of ciphers or digests
are registered as defaults, then the various EVP functions will automatically
use those implementations in preference to built in software implementations.

Although low level algorithm specific functions exist for many algorithms, their
use is discouraged. They cannot be used with an

`ENGINE`, and

`ENGINE` versions of new algorithms cannot be
accessed using the low level functions. Using them also makes code harder to
adapt to new algorithms, some options are not cleanly supported at the low
level, and some operations are more efficient using the high level interfaces.

ENGINE_register_RSA(3),

EVP_AEAD_CTX_init(3),

EVP_BytesToKey(3),

EVP_DigestInit(3),

EVP_DigestSignInit(3),

EVP_EncryptInit(3),

EVP_OpenInit(3),

EVP_PKEY_decrypt(3),

EVP_PKEY_derive(3),

EVP_PKEY_encrypt(3),

EVP_PKEY_keygen(3),

EVP_PKEY_new(3),

EVP_PKEY_print_private(3),

EVP_PKEY_set1_RSA(3),

EVP_PKEY_sign(3),

EVP_PKEY_verify(3),

EVP_PKEY_verify_recover(3),

EVP_SealInit(3),

EVP_SignInit(3),

EVP_VerifyInit(3),

OpenSSL_add_all_algorithms(3)