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".
implement digital signatures.
Symmetric encryption is available with the EVP_Encrypt...
functions. The EVP_Digest...
functions provide message digests.
functions provide a high level interface to
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.