5 EVP_PKEY_verify_recover_init, EVP_PKEY_verify_recover_init_ex,
6 EVP_PKEY_verify_recover
7 - recover signature using a public key algorithm
11 #include <openssl/evp.h>
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);
22 EVP_PKEY_verify_recover_init() initializes a public key algorithm context
23 I<ctx> for signing using the algorithm given when the context was created
24 using L<EVP_PKEY_CTX_new(3)> or variants thereof. The algorithm is used to
25 fetch a B<EVP_SIGNATURE> method implicitly, see L<provider(7)/Implicit fetch>
26 for more information about implicit fetches.
28 EVP_PKEY_verify_recover_init_ex() is the same as
29 EVP_PKEY_verify_recover_init() but additionally sets the passed parameters
30 I<params> on the context before returning.
32 The EVP_PKEY_verify_recover() function recovers signed data
33 using I<ctx>. The signature is specified using the I<sig> and
34 I<siglen> parameters. If I<rout> is NULL then the maximum size of the output
35 buffer is written to the I<routlen> parameter. If I<rout> is not NULL then
36 before the call the I<routlen> parameter should contain the length of the
37 I<rout> buffer, if the call is successful recovered data is written to
38 I<rout> and the amount of data written to I<routlen>.
42 Normally an application is only interested in whether a signature verification
43 operation is successful in those cases the EVP_verify() function should be
46 Sometimes however it is useful to obtain the data originally signed using a
47 signing operation. Only certain public key algorithms can recover a signature
48 in this way (for example RSA in PKCS padding mode).
50 After the call to EVP_PKEY_verify_recover_init() algorithm specific control
51 operations can be performed to set any appropriate parameters for the
54 The function EVP_PKEY_verify_recover() can be called more than once on the same
55 context if several operations are performed using the same parameters.
59 EVP_PKEY_verify_recover_init() and EVP_PKEY_verify_recover() return 1 for success
60 and 0 or a negative value for failure. In particular a return value of -2
61 indicates the operation is not supported by the public key algorithm.
65 Recover digest originally signed using PKCS#1 and SHA256 digest:
67 #include <openssl/evp.h>
68 #include <openssl/rsa.h>
71 unsigned char *rout, *sig;
72 size_t routlen, siglen;
76 * NB: assumes verify_key, sig and siglen are already set up
77 * and that verify_key is an RSA public key
79 ctx = EVP_PKEY_CTX_new(verify_key, NULL /* no engine */);
82 if (EVP_PKEY_verify_recover_init(ctx) <= 0)
84 if (EVP_PKEY_CTX_set_rsa_padding(ctx, RSA_PKCS1_PADDING) <= 0)
86 if (EVP_PKEY_CTX_set_signature_md(ctx, EVP_sha256()) <= 0)
89 /* Determine buffer length */
90 if (EVP_PKEY_verify_recover(ctx, NULL, &routlen, sig, siglen) <= 0)
93 rout = OPENSSL_malloc(routlen);
98 if (EVP_PKEY_verify_recover(ctx, rout, &routlen, sig, siglen) <= 0)
101 /* Recovered data is routlen bytes written to buffer rout */
105 L<EVP_PKEY_CTX_new(3)>,
106 L<EVP_PKEY_encrypt(3)>,
107 L<EVP_PKEY_decrypt(3)>,
109 L<EVP_PKEY_verify(3)>,
110 L<EVP_PKEY_derive(3)>
114 The EVP_PKEY_verify_recover_init() and EVP_PKEY_verify_recover()
115 functions were added in OpenSSL 1.0.0.
117 The EVP_PKEY_verify_recover_init_ex() function was added in OpenSSL 3.0.
121 Copyright 2013-2021 The OpenSSL Project Authors. All Rights Reserved.
123 Licensed under the Apache License 2.0 (the "License"). You may not use
124 this file except in compliance with the License. You can obtain a copy
125 in the file LICENSE in the source distribution or at
126 L<https://www.openssl.org/source/license.html>.