evp - high-level cryptographic functions
The EVP library provides a high-level interface to cryptographic functions.
provide public key
encryption and decryption to implement digital "envelopes".
functions implement digital signatures and Message Authentication Codes
(MACs). Also see the older EVP_Sign...
Symmetric encryption is available with the EVP_Encrypt...
functions. The EVP_Digest...
functions provide message digests.
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
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.
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).
implement base 64 encoding and decoding.
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. 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)
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.