evp - high-level cryptographic functions
The EVP library provides a high-level interface to cryptographic func-
EVP_Seal... and EVP_Open... provide public key encryption and decryp-
tion to implement digital "envelopes".
The EVP_DigestSign... and EVP_DigestVerify... functions implement digi-
tal 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
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 pass-
word 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
The EVP_Encode... and EVP_Decode... functions implement base 64 encod-
ing and decoding.
Algorithms are loaded with OpenSSL_add_all_algorithms(3).
All the symmetric algorithms (ciphers), digests and asymmetric algo-
rithms (public key algorithms) can be replaced by ENGINE modules pro-
viding 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 algo-
rithms 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 opera-
tions are more efficient using the high level interface.
EVP_DigestInit(3), EVP_EncryptInit(3), EVP_OpenInit(3),
EVP_SealInit(3), EVP_DigestSignInit(3), EVP_SignInit(3), EVP_Veri-
fyInit(3), EVP_EncodeInit(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),
1.0.2t 2019-09-10 evp(3)
Man(1) output converted with