NAME

       evp - high-level cryptographic functions

SYNOPSIS

        #include <openssl/evp.h>

DESCRIPTION

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

       EVP_Seal... and EVP_Open...  provide public key encryption and decryption to implement digital
       "envelopes".

       The EVP_DigestSign... and EVP_DigestVerify... functions implement digital signatures and Message
       Authentication Codes (MACs). Also see the older EVP_Sign... and EVP_Verify...  functions.

       Symmetric encryption is available with the EVP_Encrypt...  functions.  The EVP_Digest... functions
       provide message digests.

       The EVP_PKEY... functions provide a high level interface to asymmetric algorithms. To create a new
       EVP_PKEY see EVP_PKEY_new(3). EVP_PKEYs can be associated with a private key of a particular algorithm by
       using the functions described on the EVP_PKEY_set1_RSA(3) page, or new keys can be generated using
       EVP_PKEY_keygen(3).  EVP_PKEYs 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:

       For key agreement see EVP_PKEY_derive(3)
       For signing and verifying see EVP_PKEY_sign(3), EVP_PKEY_verify(3) and EVP_PKEY_verify_recover(3).
       However, note that these functions do not perform a digest of the data to be signed. Therefore normally
       you would use the EVP_DigestSign... functions for this purpose.
       For encryption and decryption see EVP_PKEY_encrypt(3) and EVP_PKEY_decrypt(3) respectively. However, note
       that these functions perform encryption and decryption only. As public key encryption is an expensive
       operation, normally you would wrap an encrypted message in a "digital envelope" using the EVP_Seal... and
       EVP_Open... functions.

       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 not typically use this (preferring, for example, PBKDF2 from PCKS#5).

       Algorithms are loaded with OpenSSL_add_all_algorithms(3).

       The EVP_Encode... and EVP_Decode... functions implement base 64 encoding and decoding.

       All  the symmetric algorithms (ciphers), digests and asymmetric algorithms (public key algorithms) can be
       replaced by ENGINE modules providing alternative implementations. If ENGINE implementations of ciphers or
       digests are registered as  defaults,  then  the  various  EVP  functions  will  automatically  use  those
       implementations  automatically  in preference to built in software implementations. For more information,
       consult the engine(3) man page.

       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.  Also makes code harder to adapt to new algorithms and  some  options  are  not  cleanly
       supported at the low level and some operations are more efficient using the high level interface.

SEE ALSO

       EVP_DigestInit(3),    EVP_EncryptInit(3),    EVP_OpenInit(3),   EVP_SealInit(3),   EVP_DigestSignInit(3),
       EVP_SignInit(3),    EVP_EncodeInit(3),    EVP_VerifyInit(3),    EVP_PKEY_new(3),    EVP_PKEY_set1_RSA(3),
       EVP_PKEY_keygen(3),       EVP_PKEY_print_private(3),       EVP_PKEY_decrypt(3),      EVP_PKEY_encrypt(3),
       EVP_PKEY_sign(3), EVP_PKEY_verify(3), EVP_PKEY_verify_recover(3), EVP_PKEY_derive(3),  EVP_BytesToKey(3),
       OpenSSL_add_all_algorithms(3), engine(3)

1.0.2g                                             2021-07-13                                          evp(3SSL)