=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.

The L<B<EVP_Seal>I<XXX>|EVP_SealInit(3)> and L<B<EVP_Open>I<XXX>|EVP_OpenInit(3)>
functions provide public key encryption and decryption to implement digital "envelopes".

The L<B<EVP_DigestSign>I<XXX>|EVP_DigestSignInit(3)> and
L<B<EVP_DigestVerify>I<XXX>|EVP_DigestVerifyInit(3)> functions implement
digital signatures and Message Authentication Codes (MACs). Also see the older
L<B<EVP_Sign>I<XXX>|EVP_SignInit(3)> and L<B<EVP_Verify>I<XXX>|EVP_VerifyInit(3)>
functions.

Symmetric encryption is available with the L<B<EVP_Encrypt>I<XXX>|EVP_EncryptInit(3)>
functions.  The L<B<EVP_Digest>I<XXX>|EVP_DigestInit(3)> functions provide message digests.

The B<EVP_PKEY>I<XXX> functions provide a high-level interface to
asymmetric algorithms. To create a new EVP_PKEY see
L<EVP_PKEY_new(3)>. EVP_PKEYs can be associated
with a private key of a particular algorithm by using the functions
described on the L<EVP_PKEY_fromdata(3)> page, or
new keys can be generated using L<EVP_PKEY_keygen(3)>.
EVP_PKEYs can be compared using L<EVP_PKEY_eq(3)>, or printed using
L<EVP_PKEY_print_private(3)>. L<EVP_PKEY_todata(3)> can be used to convert a
key back into an L<OSSL_PARAM(3)> array.

The EVP_PKEY functions support the full range of asymmetric algorithm operations:

=over 4

=item For key agreement see L<EVP_PKEY_derive(3)>

=item For signing and verifying see L<EVP_PKEY_sign(3)>,
L<EVP_PKEY_verify(3)> and L<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 L<EVP_DigestSignInit(3)>
functions for this purpose.

=item For encryption and decryption see L<EVP_PKEY_encrypt(3)>
and L<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 L<EVP_SealInit(3)> and
L<EVP_OpenInit(3)> functions.

=back

The L<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).

The L<B<EVP_Encode>I<XXX>|EVP_EncodeInit(3)> and
L<B<EVP_Decode>I<XXX>|EVP_EncodeInit(3)> functions implement base64 encoding
and decoding.

Providers can supply implementations for a wide range of cryptographic
operations, including symmetric algorithms (ciphers), digests, asymmetric
algorithms (public key algorithms), key management, parameter generation,
and more. For more information, consult the provider(7) man page.

Although low-level algorithm specific functions exist for many algorithms,
their use is discouraged. They do not call into providers such as the fips
provider and thus they are not FIPS 140-3 validated. If an accelerated
implementation of an algorithm is provided through a third party provider
the low level API will not use that implementation either.

=head1 SEE ALSO

L<EVP_DigestInit(3)>,
L<EVP_EncryptInit(3)>,
L<EVP_OpenInit(3)>,
L<EVP_SealInit(3)>,
L<EVP_DigestSignInit(3)>,
L<EVP_SignInit(3)>,
L<EVP_VerifyInit(3)>,
L<EVP_EncodeInit(3)>,
L<EVP_PKEY_new(3)>,
L<EVP_PKEY_fromdata(3)>,
L<EVP_PKEY_todata(3)>,
L<EVP_PKEY_keygen(3)>,
L<EVP_PKEY_print_private(3)>,
L<EVP_PKEY_decrypt(3)>,
L<EVP_PKEY_encrypt(3)>,
L<EVP_PKEY_sign(3)>,
L<EVP_PKEY_verify(3)>,
L<EVP_PKEY_verify_recover(3)>,
L<EVP_PKEY_derive(3)>,
L<EVP_BytesToKey(3)>,

=head1 COPYRIGHT

Copyright 2000-2025 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (the "License").  You may not use
this file except in compliance with the License.  You can obtain a copy
in the file LICENSE in the source distribution or at
L<https://www.openssl.org/source/license.html>.

=cut
