1=pod 2 3=head1 NAME 4 5EVP_PKEY_verify_recover_init, EVP_PKEY_verify_recover - recover signature using a public key algorithm 6 7=head1 SYNOPSIS 8 9 #include <openssl/evp.h> 10 11 int EVP_PKEY_verify_recover_init(EVP_PKEY_CTX *ctx); 12 int EVP_PKEY_verify_recover(EVP_PKEY_CTX *ctx, 13 unsigned char *rout, size_t *routlen, 14 const unsigned char *sig, size_t siglen); 15 16=head1 DESCRIPTION 17 18The EVP_PKEY_verify_recover_init() function initializes a public key algorithm 19context using key B<pkey> for a verify recover operation. 20 21The EVP_PKEY_verify_recover() function recovers signed data 22using B<ctx>. The signature is specified using the B<sig> and 23B<siglen> parameters. If B<rout> is B<NULL> then the maximum size of the output 24buffer is written to the B<routlen> parameter. If B<rout> is not B<NULL> then 25before the call the B<routlen> parameter should contain the length of the 26B<rout> buffer, if the call is successful recovered data is written to 27B<rout> and the amount of data written to B<routlen>. 28 29=head1 NOTES 30 31Normally an application is only interested in whether a signature verification 32operation is successful in those cases the EVP_verify() function should be 33used. 34 35Sometimes however it is useful to obtain the data originally signed using a 36signing operation. Only certain public key algorithms can recover a signature 37in this way (for example RSA in PKCS padding mode). 38 39After the call to EVP_PKEY_verify_recover_init() algorithm specific control 40operations can be performed to set any appropriate parameters for the 41operation. 42 43The function EVP_PKEY_verify_recover() can be called more than once on the same 44context if several operations are performed using the same parameters. 45 46=head1 RETURN VALUES 47 48EVP_PKEY_verify_recover_init() and EVP_PKEY_verify_recover() return 1 for success 49and 0 or a negative value for failure. In particular a return value of -2 50indicates the operation is not supported by the public key algorithm. 51 52=head1 EXAMPLES 53 54Recover digest originally signed using PKCS#1 and SHA256 digest: 55 56 #include <openssl/evp.h> 57 #include <openssl/rsa.h> 58 59 EVP_PKEY_CTX *ctx; 60 unsigned char *rout, *sig; 61 size_t routlen, siglen; 62 EVP_PKEY *verify_key; 63 64 /* 65 * NB: assumes verify_key, sig and siglen are already set up 66 * and that verify_key is an RSA public key 67 */ 68 ctx = EVP_PKEY_CTX_new(verify_key, NULL /* no engine */); 69 if (!ctx) 70 /* Error occurred */ 71 if (EVP_PKEY_verify_recover_init(ctx) <= 0) 72 /* Error */ 73 if (EVP_PKEY_CTX_set_rsa_padding(ctx, RSA_PKCS1_PADDING) <= 0) 74 /* Error */ 75 if (EVP_PKEY_CTX_set_signature_md(ctx, EVP_sha256()) <= 0) 76 /* Error */ 77 78 /* Determine buffer length */ 79 if (EVP_PKEY_verify_recover(ctx, NULL, &routlen, sig, siglen) <= 0) 80 /* Error */ 81 82 rout = OPENSSL_malloc(routlen); 83 84 if (!rout) 85 /* malloc failure */ 86 87 if (EVP_PKEY_verify_recover(ctx, rout, &routlen, sig, siglen) <= 0) 88 /* Error */ 89 90 /* Recovered data is routlen bytes written to buffer rout */ 91 92=head1 SEE ALSO 93 94L<EVP_PKEY_CTX_new(3)>, 95L<EVP_PKEY_encrypt(3)>, 96L<EVP_PKEY_decrypt(3)>, 97L<EVP_PKEY_sign(3)>, 98L<EVP_PKEY_verify(3)>, 99L<EVP_PKEY_derive(3)> 100 101=head1 HISTORY 102 103These functions were added in OpenSSL 1.0.0. 104 105=head1 COPYRIGHT 106 107Copyright 2013-2019 The OpenSSL Project Authors. All Rights Reserved. 108 109Licensed under the OpenSSL license (the "License"). You may not use 110this file except in compliance with the License. You can obtain a copy 111in the file LICENSE in the source distribution or at 112L<https://www.openssl.org/source/license.html>. 113 114=cut 115