=pod =head1 NAME EVP_PKEY_verify_recover_init, EVP_PKEY_verify_recover - recover signature using a public key algorithm =head1 SYNOPSIS #include int EVP_PKEY_verify_recover_init(EVP_PKEY_CTX *ctx); int EVP_PKEY_verify_recover(EVP_PKEY_CTX *ctx, unsigned char *rout, size_t *routlen, const unsigned char *sig, size_t siglen); =head1 DESCRIPTION The EVP_PKEY_verify_recover_init() function initializes a public key algorithm context using key B for a verify recover operation. The EVP_PKEY_verify_recover() function recovers signed data using B. The signature is specified using the B and B parameters. If B is B then the maximum size of the output buffer is written to the B parameter. If B is not B then before the call the B parameter should contain the length of the B buffer, if the call is successful recovered data is written to B and the amount of data written to B. =head1 NOTES Normally an application is only interested in whether a signature verification operation is successful in those cases the EVP_verify() function should be used. Sometimes however it is useful to obtain the data originally signed using a signing operation. Only certain public key algorithms can recover a signature in this way (for example RSA in PKCS padding mode). After the call to EVP_PKEY_verify_recover_init() algorithm specific control operations can be performed to set any appropriate parameters for the operation. The function EVP_PKEY_verify_recover() can be called more than once on the same context if several operations are performed using the same parameters. =head1 RETURN VALUES EVP_PKEY_verify_recover_init() and EVP_PKEY_verify_recover() return 1 for success and 0 or a negative value for failure. In particular a return value of -2 indicates the operation is not supported by the public key algorithm. =head1 EXAMPLE Recover digest originally signed using PKCS#1 and SHA256 digest: #include #include EVP_PKEY_CTX *ctx; unsigned char *rout, *sig; size_t routlen, siglen; EVP_PKEY *verify_key; /* * NB: assumes verify_key, sig and siglen are already set up * and that verify_key is an RSA public key */ ctx = EVP_PKEY_CTX_new(verify_key, NULL /* no engine */); if (!ctx) /* Error occurred */ if (EVP_PKEY_verify_recover_init(ctx) <= 0) /* Error */ if (EVP_PKEY_CTX_set_rsa_padding(ctx, RSA_PKCS1_PADDING) <= 0) /* Error */ if (EVP_PKEY_CTX_set_signature_md(ctx, EVP_sha256()) <= 0) /* Error */ /* Determine buffer length */ if (EVP_PKEY_verify_recover(ctx, NULL, &routlen, sig, siglen) <= 0) /* Error */ rout = OPENSSL_malloc(routlen); if (!rout) /* malloc failure */ if (EVP_PKEY_verify_recover(ctx, rout, &routlen, sig, siglen) <= 0) /* Error */ /* Recovered data is routlen bytes written to buffer rout */ =head1 SEE ALSO L, L, L, L, L, L =head1 HISTORY These functions were added in OpenSSL 1.0.0. =head1 COPYRIGHT Copyright 2013-2018 The OpenSSL Project Authors. All Rights Reserved. Licensed under the Apache License 2.0 (the "License"). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at L. =cut