NAME

       evp - high-level cryptographic functions

SYNOPSIS

        #include <openssl/evp.h>

DESCRIPTION

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

       The EVP_SealXXX and EVP_OpenXXX functions provide public key encryption and decryption to
       implement digital "envelopes".

       The EVP_DigestSignXXX and EVP_DigestVerifyXXX functions implement digital signatures and
       Message Authentication Codes (MACs). Also see the older EVP_SignXXX and EVP_VerifyXXX
       functions.

       Symmetric encryption is available with the EVP_EncryptXXX functions.  The EVP_DigestXXX
       functions provide message digests.

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

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

       For key agreement see EVP_PKEY_derive(3)
       For signing and verifying see EVP_PKEY_sign(3), EVP_PKEY_verify(3) and
       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 EVP_DigestSignInit(3)
       functions for this purpose.
       For encryption and decryption see EVP_PKEY_encrypt(3) and 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 EVP_SealInit(3) and EVP_OpenInit(3) functions.

       The 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 EVP_EncodeXXX and EVP_DecodeXXX 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.

SEE ALSO

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

COPYRIGHT

       Copyright 2000-2021 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 <https://www.openssl.org/source/license.html>.