xref: /openssl/doc/man7/evp.pod (revision 7ed6de99)
1=pod
2
3=head1 NAME
4
5evp - high-level cryptographic functions
6
7=head1 SYNOPSIS
8
9 #include <openssl/evp.h>
10
11=head1 DESCRIPTION
12
13The EVP library provides a high-level interface to cryptographic
14functions.
15
16The L<B<EVP_Seal>I<XXX>|EVP_SealInit(3)> and L<B<EVP_Open>I<XXX>|EVP_OpenInit(3)>
17functions provide public key encryption and decryption to implement digital "envelopes".
18
19The L<B<EVP_DigestSign>I<XXX>|EVP_DigestSignInit(3)> and
20L<B<EVP_DigestVerify>I<XXX>|EVP_DigestVerifyInit(3)> functions implement
21digital signatures and Message Authentication Codes (MACs). Also see the older
22L<B<EVP_Sign>I<XXX>|EVP_SignInit(3)> and L<B<EVP_Verify>I<XXX>|EVP_VerifyInit(3)>
23functions.
24
25Symmetric encryption is available with the L<B<EVP_Encrypt>I<XXX>|EVP_EncryptInit(3)>
26functions.  The L<B<EVP_Digest>I<XXX>|EVP_DigestInit(3)> functions provide message digests.
27
28The B<EVP_PKEY>I<XXX> functions provide a high-level interface to
29asymmetric algorithms. To create a new EVP_PKEY see
30L<EVP_PKEY_new(3)>. EVP_PKEYs can be associated
31with a private key of a particular algorithm by using the functions
32described on the L<EVP_PKEY_fromdata(3)> page, or
33new keys can be generated using L<EVP_PKEY_keygen(3)>.
34EVP_PKEYs can be compared using L<EVP_PKEY_eq(3)>, or printed using
35L<EVP_PKEY_print_private(3)>. L<EVP_PKEY_todata(3)> can be used to convert a
36key back into an L<OSSL_PARAM(3)> array.
37
38The EVP_PKEY functions support the full range of asymmetric algorithm operations:
39
40=over 4
41
42=item For key agreement see L<EVP_PKEY_derive(3)>
43
44=item For signing and verifying see L<EVP_PKEY_sign(3)>,
45L<EVP_PKEY_verify(3)> and L<EVP_PKEY_verify_recover(3)>.
46However, note that
47these functions do not perform a digest of the data to be signed. Therefore,
48normally you would use the L<EVP_DigestSignInit(3)>
49functions for this purpose.
50
51=item For encryption and decryption see L<EVP_PKEY_encrypt(3)>
52and L<EVP_PKEY_decrypt(3)> respectively. However, note that
53these functions perform encryption and decryption only. As public key
54encryption is an expensive operation, normally you would wrap
55an encrypted message in a "digital envelope" using the L<EVP_SealInit(3)> and
56L<EVP_OpenInit(3)> functions.
57
58=back
59
60The L<EVP_BytesToKey(3)> function provides some limited support for password
61based encryption. Careful selection of the parameters will provide a PKCS#5 PBKDF1 compatible
62implementation. However, new applications should not typically use this (preferring, for example,
63PBKDF2 from PCKS#5).
64
65The L<B<EVP_Encode>I<XXX>|EVP_EncodeInit(3)> and
66L<B<EVP_Decode>I<XXX>|EVP_EncodeInit(3)> functions implement base64 encoding
67and decoding.
68
69All the symmetric algorithms (ciphers), digests and asymmetric algorithms
70(public key algorithms) can be replaced by ENGINE modules providing alternative
71implementations. If ENGINE implementations of ciphers or digests are registered
72as defaults, then the various EVP functions will automatically use those
73implementations automatically in preference to built in software
74implementations. For more information, consult the engine(3) man page.
75
76Although low-level algorithm specific functions exist for many algorithms
77their use is discouraged. They cannot be used with an ENGINE and ENGINE
78versions of new algorithms cannot be accessed using the low-level functions.
79Also makes code harder to adapt to new algorithms and some options are not
80cleanly supported at the low-level and some operations are more efficient
81using the high-level interface.
82
83=head1 SEE ALSO
84
85L<EVP_DigestInit(3)>,
86L<EVP_EncryptInit(3)>,
87L<EVP_OpenInit(3)>,
88L<EVP_SealInit(3)>,
89L<EVP_DigestSignInit(3)>,
90L<EVP_SignInit(3)>,
91L<EVP_VerifyInit(3)>,
92L<EVP_EncodeInit(3)>,
93L<EVP_PKEY_new(3)>,
94L<EVP_PKEY_fromdata(3)>,
95L<EVP_PKEY_todata(3)>,
96L<EVP_PKEY_keygen(3)>,
97L<EVP_PKEY_print_private(3)>,
98L<EVP_PKEY_decrypt(3)>,
99L<EVP_PKEY_encrypt(3)>,
100L<EVP_PKEY_sign(3)>,
101L<EVP_PKEY_verify(3)>,
102L<EVP_PKEY_verify_recover(3)>,
103L<EVP_PKEY_derive(3)>,
104L<EVP_BytesToKey(3)>,
105L<ENGINE_by_id(3)>
106
107=head1 COPYRIGHT
108
109Copyright 2000-2024 The OpenSSL Project Authors. All Rights Reserved.
110
111Licensed under the Apache License 2.0 (the "License").  You may not use
112this file except in compliance with the License.  You can obtain a copy
113in the file LICENSE in the source distribution or at
114L<https://www.openssl.org/source/license.html>.
115
116=cut
117