mirror of https://github.com/openssl/openssl
137 lines
4.4 KiB
Plaintext
137 lines
4.4 KiB
Plaintext
=pod
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=head1 NAME
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EVP_PKEY_decrypt_init, EVP_PKEY_decrypt_init_ex,
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EVP_PKEY_decrypt - decrypt using a public key algorithm
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=head1 SYNOPSIS
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#include <openssl/evp.h>
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int EVP_PKEY_decrypt_init(EVP_PKEY_CTX *ctx);
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int EVP_PKEY_decrypt_init_ex(EVP_PKEY_CTX *ctx, const OSSL_PARAM params[]);
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int EVP_PKEY_decrypt(EVP_PKEY_CTX *ctx,
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unsigned char *out, size_t *outlen,
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const unsigned char *in, size_t inlen);
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=head1 DESCRIPTION
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The EVP_PKEY_decrypt_init() function initializes a public key algorithm
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context using key I<pkey> for a decryption operation.
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The EVP_PKEY_decrypt_init_ex() function initializes a public key algorithm
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context using key I<pkey> for a decryption operation and sets the
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algorithm specific I<params>.
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The EVP_PKEY_decrypt() function performs a public key decryption operation
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using I<ctx>. The data to be decrypted is specified using the I<in> and
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I<inlen> parameters. If I<out> is NULL then the minimum required size of
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the output buffer is written to the I<*outlen> parameter.
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If I<out> is not NULL then before the call the I<*outlen> parameter must
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contain the length of the I<out> buffer. If the call is successful the
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decrypted data is written to I<out> and the amount of the decrypted data
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written to I<*outlen>, otherwise an error is returned.
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=head1 NOTES
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After the call to EVP_PKEY_decrypt_init() algorithm specific control
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operations can be performed to set any appropriate parameters for the
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operation. These operations can be included in the EVP_PKEY_decrypt_init_ex()
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call.
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The function EVP_PKEY_decrypt() can be called more than once on the same
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context if several operations are performed using the same parameters.
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=head1 RETURN VALUES
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EVP_PKEY_decrypt_init(), EVP_PKEY_decrypt_init_ex() and EVP_PKEY_decrypt()
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return 1 for success and 0 or a negative value for failure. In particular a
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return value of -2 indicates the operation is not supported by the public key
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algorithm.
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=head1 WARNINGS
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In OpenSSL versions before 3.2.0, when used in PKCS#1 v1.5 padding,
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both the return value from the EVP_PKEY_decrypt() and the B<outlen> provided
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information useful in mounting a Bleichenbacher attack against the
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used private key. They had to be processed in a side-channel free way.
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Since version 3.2.0, the EVP_PKEY_decrypt() method when used with PKCS#1
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v1.5 padding as implemented in the B<default> provider implements
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the implicit rejection mechanism (see
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B<OSSL_PKEY_PARAM_IMPLICIT_REJECTION> in L<provider-asym_cipher(7)>).
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That means it doesn't return an error when it detects an error in padding,
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instead it returns a pseudo-randomly generated message, removing the need
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of side-channel secure code from applications using OpenSSL.
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If OpenSSL is configured to use a provider that doesn't implement implicit
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rejection, the code still needs to handle the returned values
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using side-channel free code.
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Side-channel free handling of the error stack can be performed using
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either a pair of unconditional L<ERR_set_mark(3)> and L<ERR_pop_to_mark(3)>
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calls or by using the L<ERR_clear_error(3)> call.
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=head1 EXAMPLES
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Decrypt data using OAEP (for RSA keys):
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#include <openssl/evp.h>
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#include <openssl/rsa.h>
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EVP_PKEY_CTX *ctx;
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ENGINE *eng;
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unsigned char *out, *in;
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size_t outlen, inlen;
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EVP_PKEY *key;
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/*
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* NB: assumes key, eng, in, inlen are already set up
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* and that key is an RSA private key
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*/
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ctx = EVP_PKEY_CTX_new(key, eng);
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if (!ctx)
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/* Error occurred */
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if (EVP_PKEY_decrypt_init(ctx) <= 0)
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/* Error */
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if (EVP_PKEY_CTX_set_rsa_padding(ctx, RSA_PKCS1_OAEP_PADDING) <= 0)
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/* Error */
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/* Determine buffer length */
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if (EVP_PKEY_decrypt(ctx, NULL, &outlen, in, inlen) <= 0)
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/* Error */
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out = OPENSSL_malloc(outlen);
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if (!out)
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/* malloc failure */
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if (EVP_PKEY_decrypt(ctx, out, &outlen, in, inlen) <= 0)
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/* Error */
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/* Decrypted data is outlen bytes written to buffer out */
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=head1 SEE ALSO
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L<EVP_PKEY_CTX_new(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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=head1 HISTORY
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These functions were added in OpenSSL 1.0.0.
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=head1 COPYRIGHT
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Copyright 2006-2021 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the Apache License 2.0 (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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