openssl/doc/crypto/evp.pod

=pod

=head1 NAME

evp - high-level cryptographic functions

=head1 SYNOPSIS

 #include <openssl/evp.h>

=head1 DESCRIPTION

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

B<EVP_Seal>I<...> and B<EVP_Open>I<...> provide public key encryption
and decryption to implement digital "envelopes".

The B<EVP_Sign>I<...> and B<EVP_Verify>I<...> functions implement
digital signatures.

Symmetric encryption is available with the B<EVP_Encrypt>I<...>
functions.  The B<EVP_Digest>I<...> functions provide message digests.

The B<EVP_PKEY>I<...> functions provide a high level interface to
asymmetric algorithms.

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) 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.

=head1 SEE ALSO

L<EVP_DigestInit(3)|EVP_DigestInit(3)>,
L<EVP_EncryptInit(3)|EVP_EncryptInit(3)>,
L<EVP_OpenInit(3)|EVP_OpenInit(3)>,
L<EVP_SealInit(3)|EVP_SealInit(3)>,
L<EVP_SignInit(3)|EVP_SignInit(3)>,
L<EVP_VerifyInit(3)|EVP_VerifyInit(3)>,
L<OpenSSL_add_all_algorithms(3)|OpenSSL_add_all_algorithms(3)>,
L<engine(3)|engine(3)>

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