Openssl 1.1.0h
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=pod
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=for comment openssl_manual_section:7
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=head1 NAME
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evp - high-level cryptographic functions
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=head1 SYNOPSIS
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#include <openssl/evp.h>
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=head1 DESCRIPTION
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The EVP library provides a high-level interface to cryptographic
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functions.
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L<B<EVP_Seal>I<...>|EVP_SealInit(3)> and L<B<EVP_Open>I<...>|EVP_OpenInit(3)>
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provide public key encryption and decryption to implement digital "envelopes".
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The L<B<EVP_DigestSign>I<...>|EVP_DigestSignInit(3)> and
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L<B<EVP_DigestVerify>I<...>|EVP_DigestVerifyInit(3)> functions implement
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digital signatures and Message Authentication Codes (MACs). Also see the older
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L<B<EVP_Sign>I<...>|EVP_SignInit(3)> and L<B<EVP_Verify>I<...>|EVP_VerifyInit(3)>
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functions.
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Symmetric encryption is available with the L<B<EVP_Encrypt>I<...>|EVP_EncryptInit(3)>
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functions. The L<B<EVP_Digest>I<...>|EVP_DigestInit(3)> functions provide message digests.
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The B<EVP_PKEY>I<...> functions provide a high level interface to
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asymmetric algorithms. To create a new EVP_PKEY see
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L<EVP_PKEY_new(3)>. EVP_PKEYs can be associated
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with a private key of a particular algorithm by using the functions
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described on the L<EVP_PKEY_set1_RSA(3)> page, or
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new keys can be generated using L<EVP_PKEY_keygen(3)>.
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EVP_PKEYs can be compared using L<EVP_PKEY_cmp(3)>, or printed using
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L<EVP_PKEY_print_private(3)>.
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The EVP_PKEY functions support the full range of asymmetric algorithm operations:
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=over 4
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=item For key agreement see L<EVP_PKEY_derive(3)>
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=item For signing and verifying see L<EVP_PKEY_sign(3)>,
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L<EVP_PKEY_verify(3)> and L<EVP_PKEY_verify_recover(3)>.
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However, note that
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these functions do not perform a digest of the data to be signed. Therefore
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normally you would use the L<EVP_DigestSignInit(3)>
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functions for this purpose.
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=item For encryption and decryption see L<EVP_PKEY_encrypt(3)>
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and L<EVP_PKEY_decrypt(3)> respectively. However, note that
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these functions perform encryption and decryption only. As public key
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encryption is an expensive operation, normally you would wrap
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an encrypted message in a "digital envelope" using the L<EVP_SealInit(3)> and
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L<EVP_OpenInit(3)> functions.
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=back
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The L<EVP_BytesToKey(3)> function provides some limited support for password
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based encryption. Careful selection of the parameters will provide a PKCS#5 PBKDF1 compatible
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implementation. However, new applications should not typically use this (preferring, for example,
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PBKDF2 from PCKS#5).
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The L<B<EVP_Encode>I<...>|EVP_EncodeInit(3)> and
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L<B<EVP_Decode>I<...>|EVP_EncodeInit(3)> functions implement base 64 encoding
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and decoding.
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All the symmetric algorithms (ciphers), digests and asymmetric algorithms
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(public key algorithms) can be replaced by L<engine(3)> modules providing alternative
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implementations. If ENGINE implementations of ciphers or digests are registered
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as defaults, then the various EVP functions will automatically use those
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implementations automatically in preference to built in software
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implementations. For more information, consult the engine(3) man page.
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Although low level algorithm specific functions exist for many algorithms
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their use is discouraged. They cannot be used with an ENGINE and ENGINE
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versions of new algorithms cannot be accessed using the low level functions.
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Also makes code harder to adapt to new algorithms and some options are not
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cleanly supported at the low level and some operations are more efficient
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using the high level interface.
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=head1 SEE ALSO
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L<EVP_DigestInit(3)>,
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L<EVP_EncryptInit(3)>,
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L<EVP_OpenInit(3)>,
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L<EVP_SealInit(3)>,
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L<EVP_DigestSignInit(3)>,
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L<EVP_SignInit(3)>,
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L<EVP_VerifyInit(3)>,
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L<EVP_EncodeInit(3)>,
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L<EVP_PKEY_new(3)>,
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L<EVP_PKEY_set1_RSA(3)>,
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L<EVP_PKEY_keygen(3)>,
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L<EVP_PKEY_print_private(3)>,
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L<EVP_PKEY_decrypt(3)>,
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L<EVP_PKEY_encrypt(3)>,
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L<EVP_PKEY_sign(3)>,
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L<EVP_PKEY_verify(3)>,
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L<EVP_PKEY_verify_recover(3)>,
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L<EVP_PKEY_derive(3)>,
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L<EVP_BytesToKey(3)>,
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L<engine(3)>
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=head1 COPYRIGHT
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Copyright 2000-2016 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the OpenSSL license (the "License"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file LICENSE in the source distribution or at
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L<https://www.openssl.org/source/license.html>.
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=cut
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