=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_set1_RSA(3)> page, or

new keys can be generated using L<EVP_PKEY_keygen(3)>.

EVP_PKEYs can be compared using L<EVP_PKEY_cmp(3)>, or printed using

L<EVP_PKEY_print_private(3)>.

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 base 64 encoding

and decoding.

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)>,

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_set1_RSA(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)>,

L<ENGINE_by_id(3)>

=head1 COPYRIGHT

Copyright 2000-2018 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the OpenSSL license (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>.

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