1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
|
.\" -*- mode: troff; coding: utf-8 -*-
.\" Automatically generated by Pod::Man 5.01 (Pod::Simple 3.43)
.\"
.\" Standard preamble:
.\" ========================================================================
.de Sp \" Vertical space (when we can't use .PP)
.if t .sp .5v
.if n .sp
..
.de Vb \" Begin verbatim text
.ft CW
.nf
.ne \\$1
..
.de Ve \" End verbatim text
.ft R
.fi
..
.\" \*(C` and \*(C' are quotes in nroff, nothing in troff, for use with C<>.
.ie n \{\
. ds C` ""
. ds C' ""
'br\}
.el\{\
. ds C`
. ds C'
'br\}
.\"
.\" Escape single quotes in literal strings from groff's Unicode transform.
.ie \n(.g .ds Aq \(aq
.el .ds Aq '
.\"
.\" If the F register is >0, we'll generate index entries on stderr for
.\" titles (.TH), headers (.SH), subsections (.SS), items (.Ip), and index
.\" entries marked with X<> in POD. Of course, you'll have to process the
.\" output yourself in some meaningful fashion.
.\"
.\" Avoid warning from groff about undefined register 'F'.
.de IX
..
.nr rF 0
.if \n(.g .if rF .nr rF 1
.if (\n(rF:(\n(.g==0)) \{\
. if \nF \{\
. de IX
. tm Index:\\$1\t\\n%\t"\\$2"
..
. if !\nF==2 \{\
. nr % 0
. nr F 2
. \}
. \}
.\}
.rr rF
.\" ========================================================================
.\"
.IX Title "EVP_PKEY_VERIFY_RECOVER 3SSL"
.TH EVP_PKEY_VERIFY_RECOVER 3SSL 2024-02-03 3.1.5 OpenSSL
.\" For nroff, turn off justification. Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH NAME
EVP_PKEY_verify_recover_init, EVP_PKEY_verify_recover_init_ex,
EVP_PKEY_verify_recover
\&\- recover signature using a public key algorithm
.SH SYNOPSIS
.IX Header "SYNOPSIS"
.Vb 1
\& #include <openssl/evp.h>
\&
\& int EVP_PKEY_verify_recover_init(EVP_PKEY_CTX *ctx);
\& int EVP_PKEY_verify_recover_init_ex(EVP_PKEY_CTX *ctx,
\& const OSSL_PARAM params[]);
\& int EVP_PKEY_verify_recover(EVP_PKEY_CTX *ctx,
\& unsigned char *rout, size_t *routlen,
\& const unsigned char *sig, size_t siglen);
.Ve
.SH DESCRIPTION
.IX Header "DESCRIPTION"
\&\fBEVP_PKEY_verify_recover_init()\fR initializes a public key algorithm context
\&\fIctx\fR for signing using the algorithm given when the context was created
using \fBEVP_PKEY_CTX_new\fR\|(3) or variants thereof. The algorithm is used to
fetch a \fBEVP_SIGNATURE\fR method implicitly, see "Implicit fetch" in \fBprovider\fR\|(7)
for more information about implicit fetches.
.PP
\&\fBEVP_PKEY_verify_recover_init_ex()\fR is the same as
\&\fBEVP_PKEY_verify_recover_init()\fR but additionally sets the passed parameters
\&\fIparams\fR on the context before returning.
.PP
The \fBEVP_PKEY_verify_recover()\fR function recovers signed data
using \fIctx\fR. The signature is specified using the \fIsig\fR and
\&\fIsiglen\fR parameters. If \fIrout\fR is NULL then the maximum size of the output
buffer is written to the \fIroutlen\fR parameter. If \fIrout\fR is not NULL then
before the call the \fIroutlen\fR parameter should contain the length of the
\&\fIrout\fR buffer, if the call is successful recovered data is written to
\&\fIrout\fR and the amount of data written to \fIroutlen\fR.
.SH NOTES
.IX Header "NOTES"
Normally an application is only interested in whether a signature verification
operation is successful in those cases the \fBEVP_verify()\fR function should be
used.
.PP
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).
.PP
After the call to \fBEVP_PKEY_verify_recover_init()\fR algorithm specific control
operations can be performed to set any appropriate parameters for the
operation.
.PP
The function \fBEVP_PKEY_verify_recover()\fR can be called more than once on the same
context if several operations are performed using the same parameters.
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
\&\fBEVP_PKEY_verify_recover_init()\fR and \fBEVP_PKEY_verify_recover()\fR 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.
.SH EXAMPLES
.IX Header "EXAMPLES"
Recover digest originally signed using PKCS#1 and SHA256 digest:
.PP
.Vb 2
\& #include <openssl/evp.h>
\& #include <openssl/rsa.h>
\&
\& 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 */
.Ve
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBEVP_PKEY_CTX_new\fR\|(3),
\&\fBEVP_PKEY_encrypt\fR\|(3),
\&\fBEVP_PKEY_decrypt\fR\|(3),
\&\fBEVP_PKEY_sign\fR\|(3),
\&\fBEVP_PKEY_verify\fR\|(3),
\&\fBEVP_PKEY_derive\fR\|(3)
.SH HISTORY
.IX Header "HISTORY"
The \fBEVP_PKEY_verify_recover_init()\fR and \fBEVP_PKEY_verify_recover()\fR
functions were added in OpenSSL 1.0.0.
.PP
The \fBEVP_PKEY_verify_recover_init_ex()\fR function was added in OpenSSL 3.0.
.SH COPYRIGHT
.IX Header "COPYRIGHT"
Copyright 2013\-2021 The OpenSSL Project Authors. All Rights Reserved.
.PP
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
<https://www.openssl.org/source/license.html>.
|
