1=pod 2 3=head1 NAME 4 5EVP_PKEY_verify_recover_init, EVP_PKEY_verify_recover_init_ex, 6EVP_PKEY_verify_recover 7- recover signature using a public key algorithm 8 9=head1 SYNOPSIS 10 11 #include <openssl/evp.h> 12 13 int EVP_PKEY_verify_recover_init(EVP_PKEY_CTX *ctx); 14 int EVP_PKEY_verify_recover_init_ex(EVP_PKEY_CTX *ctx, 15 const OSSL_PARAM params[]); 16 int EVP_PKEY_verify_recover(EVP_PKEY_CTX *ctx, 17 unsigned char *rout, size_t *routlen, 18 const unsigned char *sig, size_t siglen); 19 20=head1 DESCRIPTION 21 22EVP_PKEY_verify_recover_init() initializes a public key algorithm context 23I<ctx> for signing using the algorithm given when the context was created 24using L<EVP_PKEY_CTX_new(3)> or variants thereof. The algorithm is used to 25fetch a B<EVP_SIGNATURE> method implicitly, see L<provider(7)/Implicit fetch> 26for more information about implicit fetches. 27 28EVP_PKEY_verify_recover_init_ex() is the same as 29EVP_PKEY_verify_recover_init() but additionally sets the passed parameters 30I<params> on the context before returning. 31 32The EVP_PKEY_verify_recover() function recovers signed data 33using I<ctx>. The signature is specified using the I<sig> and 34I<siglen> parameters. If I<rout> is NULL then the maximum size of the output 35buffer is written to the I<routlen> parameter. If I<rout> is not NULL then 36before the call the I<routlen> parameter should contain the length of the 37I<rout> buffer, if the call is successful recovered data is written to 38I<rout> and the amount of data written to I<routlen>. 39 40=head1 NOTES 41 42Normally an application is only interested in whether a signature verification 43operation is successful in those cases the EVP_verify() function should be 44used. 45 46Sometimes however it is useful to obtain the data originally signed using a 47signing operation. Only certain public key algorithms can recover a signature 48in this way (for example RSA in PKCS padding mode). 49 50After the call to EVP_PKEY_verify_recover_init() algorithm specific control 51operations can be performed to set any appropriate parameters for the 52operation. 53 54The function EVP_PKEY_verify_recover() can be called more than once on the same 55context if several operations are performed using the same parameters. 56 57=head1 RETURN VALUES 58 59EVP_PKEY_verify_recover_init() and EVP_PKEY_verify_recover() return 1 for success 60and 0 or a negative value for failure. In particular a return value of -2 61indicates the operation is not supported by the public key algorithm. 62 63=head1 EXAMPLES 64 65Recover digest originally signed using PKCS#1 and SHA256 digest: 66 67 #include <openssl/evp.h> 68 #include <openssl/rsa.h> 69 70 EVP_PKEY_CTX *ctx; 71 unsigned char *rout, *sig; 72 size_t routlen, siglen; 73 EVP_PKEY *verify_key; 74 75 /* 76 * NB: assumes verify_key, sig and siglen are already set up 77 * and that verify_key is an RSA public key 78 */ 79 ctx = EVP_PKEY_CTX_new(verify_key, NULL /* no engine */); 80 if (!ctx) 81 /* Error occurred */ 82 if (EVP_PKEY_verify_recover_init(ctx) <= 0) 83 /* Error */ 84 if (EVP_PKEY_CTX_set_rsa_padding(ctx, RSA_PKCS1_PADDING) <= 0) 85 /* Error */ 86 if (EVP_PKEY_CTX_set_signature_md(ctx, EVP_sha256()) <= 0) 87 /* Error */ 88 89 /* Determine buffer length */ 90 if (EVP_PKEY_verify_recover(ctx, NULL, &routlen, sig, siglen) <= 0) 91 /* Error */ 92 93 rout = OPENSSL_malloc(routlen); 94 95 if (!rout) 96 /* malloc failure */ 97 98 if (EVP_PKEY_verify_recover(ctx, rout, &routlen, sig, siglen) <= 0) 99 /* Error */ 100 101 /* Recovered data is routlen bytes written to buffer rout */ 102 103=head1 SEE ALSO 104 105L<EVP_PKEY_CTX_new(3)>, 106L<EVP_PKEY_encrypt(3)>, 107L<EVP_PKEY_decrypt(3)>, 108L<EVP_PKEY_sign(3)>, 109L<EVP_PKEY_verify(3)>, 110L<EVP_PKEY_derive(3)> 111 112=head1 HISTORY 113 114The EVP_PKEY_verify_recover_init() and EVP_PKEY_verify_recover() 115functions were added in OpenSSL 1.0.0. 116 117The EVP_PKEY_verify_recover_init_ex() function was added in OpenSSL 3.0. 118 119=head1 COPYRIGHT 120 121Copyright 2013-2021 The OpenSSL Project Authors. All Rights Reserved. 122 123Licensed under the Apache License 2.0 (the "License"). You may not use 124this file except in compliance with the License. You can obtain a copy 125in the file LICENSE in the source distribution or at 126L<https://www.openssl.org/source/license.html>. 127 128=cut 129