5 EVP_PKEY_verify_recover_init, EVP_PKEY_verify_recover
6 - recover signature using a public key algorithm
10 #include <openssl/evp.h>
12 int EVP_PKEY_verify_recover_init(EVP_PKEY_CTX *ctx);
13 int EVP_PKEY_verify_recover(EVP_PKEY_CTX *ctx,
14 unsigned char *rout, size_t *routlen,
15 const unsigned char *sig, size_t siglen);
19 EVP_PKEY_verify_recover_init() initializes a public key algorithm context
20 I<ctx> for signing using the algorithm given when the context was created
21 using L<EVP_PKEY_CTX_new(3)> or variants thereof. The algorithm is used to
22 fetch a B<EVP_SIGNATURE> method implicitly, see L<provider(7)/Implicit fetch>
23 for more information about implicit fetches.
25 The EVP_PKEY_verify_recover() function recovers signed data
26 using I<ctx>. The signature is specified using the I<sig> and
27 I<siglen> parameters. If I<rout> is NULL then the maximum size of the output
28 buffer is written to the I<routlen> parameter. If I<rout> is not NULL then
29 before the call the I<routlen> parameter should contain the length of the
30 I<rout> buffer, if the call is successful recovered data is written to
31 I<rout> and the amount of data written to I<routlen>.
35 Normally an application is only interested in whether a signature verification
36 operation is successful in those cases the EVP_verify() function should be
39 Sometimes however it is useful to obtain the data originally signed using a
40 signing operation. Only certain public key algorithms can recover a signature
41 in this way (for example RSA in PKCS padding mode).
43 After the call to EVP_PKEY_verify_recover_init() algorithm specific control
44 operations can be performed to set any appropriate parameters for the
47 The function EVP_PKEY_verify_recover() can be called more than once on the same
48 context if several operations are performed using the same parameters.
52 EVP_PKEY_verify_recover_init() and EVP_PKEY_verify_recover() return 1 for success
53 and 0 or a negative value for failure. In particular a return value of -2
54 indicates the operation is not supported by the public key algorithm.
58 Recover digest originally signed using PKCS#1 and SHA256 digest:
60 #include <openssl/evp.h>
61 #include <openssl/rsa.h>
64 unsigned char *rout, *sig;
65 size_t routlen, siglen;
69 * NB: assumes verify_key, sig and siglen are already set up
70 * and that verify_key is an RSA public key
72 ctx = EVP_PKEY_CTX_new(verify_key, NULL /* no engine */);
75 if (EVP_PKEY_verify_recover_init(ctx) <= 0)
77 if (EVP_PKEY_CTX_set_rsa_padding(ctx, RSA_PKCS1_PADDING) <= 0)
79 if (EVP_PKEY_CTX_set_signature_md(ctx, EVP_sha256()) <= 0)
82 /* Determine buffer length */
83 if (EVP_PKEY_verify_recover(ctx, NULL, &routlen, sig, siglen) <= 0)
86 rout = OPENSSL_malloc(routlen);
91 if (EVP_PKEY_verify_recover(ctx, rout, &routlen, sig, siglen) <= 0)
94 /* Recovered data is routlen bytes written to buffer rout */
98 L<EVP_PKEY_CTX_new(3)>,
99 L<EVP_PKEY_encrypt(3)>,
100 L<EVP_PKEY_decrypt(3)>,
102 L<EVP_PKEY_verify(3)>,
103 L<EVP_PKEY_derive(3)>
107 These functions were added in OpenSSL 1.0.0.
111 Copyright 2013-2018 The OpenSSL Project Authors. All Rights Reserved.
113 Licensed under the Apache License 2.0 (the "License"). You may not use
114 this file except in compliance with the License. You can obtain a copy
115 in the file LICENSE in the source distribution or at
116 L<https://www.openssl.org/source/license.html>.