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