mirror of https://github.com/openssl/openssl
119 lines
3.7 KiB
Plaintext
119 lines
3.7 KiB
Plaintext
=pod
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=head1 NAME
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EVP_PKEY_verify_recover_init, EVP_PKEY_verify_recover
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- recover signature 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_verify_recover_init(EVP_PKEY_CTX *ctx);
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int EVP_PKEY_verify_recover(EVP_PKEY_CTX *ctx,
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unsigned char *rout, size_t *routlen,
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const unsigned char *sig, size_t siglen);
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=head1 DESCRIPTION
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EVP_PKEY_verify_recover_init() initializes a public key algorithm context
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I<ctx> for signing using the algorithm given when the context was created
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using L<EVP_PKEY_CTX_new(3)> or variants thereof. The algorithm is used to
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fetch a B<EVP_SIGNATURE> method implicitly, see L<provider(7)/Implicit fetch>
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for more information about implicit fetches.
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The EVP_PKEY_verify_recover() function recovers signed data
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using I<ctx>. The signature is specified using the I<sig> and
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I<siglen> parameters. If I<rout> is NULL then the maximum size of the output
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buffer is written to the I<routlen> parameter. If I<rout> is not NULL then
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before the call the I<routlen> parameter should contain the length of the
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I<rout> buffer, if the call is successful recovered data is written to
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I<rout> and the amount of data written to I<routlen>.
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=head1 NOTES
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Normally an application is only interested in whether a signature verification
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operation is successful in those cases the EVP_verify() function should be
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used.
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Sometimes however it is useful to obtain the data originally signed using a
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signing operation. Only certain public key algorithms can recover a signature
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in this way (for example RSA in PKCS padding mode).
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After the call to EVP_PKEY_verify_recover_init() algorithm specific control
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operations can be performed to set any appropriate parameters for the
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operation.
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The function EVP_PKEY_verify_recover() 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_verify_recover_init() and EVP_PKEY_verify_recover() return 1 for success
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and 0 or a negative value for failure. In particular a return value of -2
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indicates the operation is not supported by the public key algorithm.
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=head1 EXAMPLES
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Recover digest originally signed using PKCS#1 and SHA256 digest:
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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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unsigned char *rout, *sig;
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size_t routlen, siglen;
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EVP_PKEY *verify_key;
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/*
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* NB: assumes verify_key, sig and siglen are already set up
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* and that verify_key is an RSA public key
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*/
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ctx = EVP_PKEY_CTX_new(verify_key, NULL /* no engine */);
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if (!ctx)
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/* Error occurred */
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if (EVP_PKEY_verify_recover_init(ctx) <= 0)
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/* Error */
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if (EVP_PKEY_CTX_set_rsa_padding(ctx, RSA_PKCS1_PADDING) <= 0)
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/* Error */
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if (EVP_PKEY_CTX_set_signature_md(ctx, EVP_sha256()) <= 0)
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/* Error */
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/* Determine buffer length */
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if (EVP_PKEY_verify_recover(ctx, NULL, &routlen, sig, siglen) <= 0)
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/* Error */
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rout = OPENSSL_malloc(routlen);
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if (!rout)
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/* malloc failure */
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if (EVP_PKEY_verify_recover(ctx, rout, &routlen, sig, siglen) <= 0)
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/* Error */
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/* Recovered data is routlen bytes written to buffer rout */
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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_decrypt(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_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 2013-2020 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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