1EVP_PKEY_VERIFY_RECOVER(3ossl)      OpenSSL     EVP_PKEY_VERIFY_RECOVER(3ossl)
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NAME

6       EVP_PKEY_verify_recover_init, EVP_PKEY_verify_recover_init_ex,
7       EVP_PKEY_verify_recover - recover signature using a public key
8       algorithm
9

SYNOPSIS

11        #include <openssl/evp.h>
12
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);
19

DESCRIPTION

21       EVP_PKEY_verify_recover_init() initializes a public key algorithm
22       context ctx for signing using the algorithm given when the context was
23       created using EVP_PKEY_CTX_new(3) or variants thereof.  The algorithm
24       is used to fetch a EVP_SIGNATURE method implicitly, see "Implicit
25       fetch" in provider(7) for more information about implicit fetches.
26
27       EVP_PKEY_verify_recover_init_ex() is the same as
28       EVP_PKEY_verify_recover_init() but additionally sets the passed
29       parameters params on the context before returning.
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31       The EVP_PKEY_verify_recover() function recovers signed data using ctx.
32       The signature is specified using the sig and siglen parameters. If rout
33       is NULL then the maximum size of the output buffer is written to the
34       routlen parameter. If rout is not NULL then before the call the routlen
35       parameter should contain the length of the rout buffer, if the call is
36       successful recovered data is written to rout and the amount of data
37       written to routlen.
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NOTES

40       Normally an application is only interested in whether a signature
41       verification operation is successful in those cases the EVP_verify()
42       function should be used.
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44       Sometimes however it is useful to obtain the data originally signed
45       using a signing operation. Only certain public key algorithms can
46       recover a signature in this way (for example RSA in PKCS padding mode).
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48       After the call to EVP_PKEY_verify_recover_init() algorithm specific
49       control operations can be performed to set any appropriate parameters
50       for the operation.
51
52       The function EVP_PKEY_verify_recover() can be called more than once on
53       the same context if several operations are performed using the same
54       parameters.
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RETURN VALUES

57       EVP_PKEY_verify_recover_init() and EVP_PKEY_verify_recover() return 1
58       for success and 0 or a negative value for failure. In particular a
59       return value of -2 indicates the operation is not supported by the
60       public key algorithm.
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EXAMPLES

63       Recover digest originally signed using PKCS#1 and SHA256 digest:
64
65        #include <openssl/evp.h>
66        #include <openssl/rsa.h>
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68        EVP_PKEY_CTX *ctx;
69        unsigned char *rout, *sig;
70        size_t routlen, siglen;
71        EVP_PKEY *verify_key;
72
73        /*
74         * NB: assumes verify_key, sig and siglen are already set up
75         * and that verify_key is an RSA public key
76         */
77        ctx = EVP_PKEY_CTX_new(verify_key, NULL /* no engine */);
78        if (!ctx)
79            /* Error occurred */
80        if (EVP_PKEY_verify_recover_init(ctx) <= 0)
81            /* Error */
82        if (EVP_PKEY_CTX_set_rsa_padding(ctx, RSA_PKCS1_PADDING) <= 0)
83            /* Error */
84        if (EVP_PKEY_CTX_set_signature_md(ctx, EVP_sha256()) <= 0)
85            /* Error */
86
87        /* Determine buffer length */
88        if (EVP_PKEY_verify_recover(ctx, NULL, &routlen, sig, siglen) <= 0)
89            /* Error */
90
91        rout = OPENSSL_malloc(routlen);
92
93        if (!rout)
94            /* malloc failure */
95
96        if (EVP_PKEY_verify_recover(ctx, rout, &routlen, sig, siglen) <= 0)
97            /* Error */
98
99        /* Recovered data is routlen bytes written to buffer rout */
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SEE ALSO

102       EVP_PKEY_CTX_new(3), EVP_PKEY_encrypt(3), EVP_PKEY_decrypt(3),
103       EVP_PKEY_sign(3), EVP_PKEY_verify(3), EVP_PKEY_derive(3)
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HISTORY

106       The EVP_PKEY_verify_recover_init() and EVP_PKEY_verify_recover()
107       functions were added in OpenSSL 1.0.0.
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109       The EVP_PKEY_verify_recover_init_ex() function was added in OpenSSL
110       3.0.
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113       Copyright 2013-2021 The OpenSSL Project Authors. All Rights Reserved.
114
115       Licensed under the Apache License 2.0 (the "License").  You may not use
116       this file except in compliance with the License.  You can obtain a copy
117       in the file LICENSE in the source distribution or at
118       <https://www.openssl.org/source/license.html>.
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1223.0.5                             2022-07-05    EVP_PKEY_VERIFY_RECOVER(3ossl)
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