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 EXAMPLE 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 /* NB: assumes verify_key, sig and siglen are already set up 64 * and that verify_key is an RSA public key 65 */ 66 ctx = EVP_PKEY_CTX_new(verify_key); 67 if (!ctx) 68 /* Error occurred */ 69 if (EVP_PKEY_verify_recover_init(ctx) <= 0) 70 /* Error */ 71 if (EVP_PKEY_CTX_set_rsa_padding(ctx, RSA_PKCS1_PADDING) <= 0) 72 /* Error */ 73 if (EVP_PKEY_CTX_set_signature_md(ctx, EVP_sha256()) <= 0) 74 /* Error */ 75 76 /* Determine buffer length */ 77 if (EVP_PKEY_verify_recover(ctx, NULL, &routlen, sig, siglen) <= 0) 78 /* Error */ 79 80 rout = OPENSSL_malloc(routlen); 81 82 if (!rout) 83 /* malloc failure */ 84 85 if (EVP_PKEY_verify_recover(ctx, rout, &routlen, sig, siglen) <= 0) 86 /* Error */ 87 88 /* Recovered data is routlen bytes written to buffer rout */ 89 90=head1 SEE ALSO 91 92L<EVP_PKEY_CTX_new(3)|EVP_PKEY_CTX_new(3)>, 93L<EVP_PKEY_encrypt(3)|EVP_PKEY_encrypt(3)>, 94L<EVP_PKEY_decrypt(3)|EVP_PKEY_decrypt(3)>, 95L<EVP_PKEY_sign(3)|EVP_PKEY_sign(3)>, 96L<EVP_PKEY_verify(3)|EVP_PKEY_verify(3)>, 97L<EVP_PKEY_derive(3)|EVP_PKEY_derive(3)> 98 99=head1 HISTORY 100 101These functions were first added to OpenSSL 1.0.0. 102 103=cut 104