232 lines
7.3 KiB
Groff
232 lines
7.3 KiB
Groff
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.\" ========================================================================
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.\"
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.IX Title "EVP_PKEY_verify_recover 3"
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.TH EVP_PKEY_verify_recover 3 "2017-05-25" "1.0.2l" "OpenSSL"
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.\" For nroff, turn off justification. Always turn off hyphenation; it makes
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.\" way too many mistakes in technical documents.
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.if n .ad l
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.nh
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.SH "NAME"
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EVP_PKEY_verify_recover_init, EVP_PKEY_verify_recover \- recover signature using a public key algorithm
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.SH "SYNOPSIS"
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.IX Header "SYNOPSIS"
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.Vb 1
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\& #include <openssl/evp.h>
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\&
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\& int EVP_PKEY_verify_recover_init(EVP_PKEY_CTX *ctx);
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\& int EVP_PKEY_verify_recover(EVP_PKEY_CTX *ctx,
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\& unsigned char *rout, size_t *routlen,
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\& const unsigned char *sig, size_t siglen);
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.Ve
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.SH "DESCRIPTION"
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.IX Header "DESCRIPTION"
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The \fIEVP_PKEY_verify_recover_init()\fR function initializes a public key algorithm
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context using key \fBpkey\fR for a verify recover operation.
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.PP
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The \fIEVP_PKEY_verify_recover()\fR function recovers signed data
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using \fBctx\fR. The signature is specified using the \fBsig\fR and
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\&\fBsiglen\fR parameters. If \fBrout\fR is \fB\s-1NULL\s0\fR then the maximum size of the output
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buffer is written to the \fBroutlen\fR parameter. If \fBrout\fR is not \fB\s-1NULL\s0\fR then
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before the call the \fBroutlen\fR parameter should contain the length of the
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\&\fBrout\fR buffer, if the call is successful recovered data is written to
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\&\fBrout\fR and the amount of data written to \fBroutlen\fR.
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.SH "NOTES"
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.IX Header "NOTES"
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Normally an application is only interested in whether a signature verification
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operation is successful in those cases the \fIEVP_verify()\fR function should be
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used.
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.PP
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Sometimes however it is useful to obtain the data originally signed using a
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signing operation. Only certain public key algorithms can recover a signature
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in this way (for example \s-1RSA\s0 in \s-1PKCS\s0 padding mode).
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.PP
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After the call to \fIEVP_PKEY_verify_recover_init()\fR algorithm specific control
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operations can be performed to set any appropriate parameters for the
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operation.
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.PP
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The function \fIEVP_PKEY_verify_recover()\fR can be called more than once on the same
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context if several operations are performed using the same parameters.
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.SH "RETURN VALUES"
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.IX Header "RETURN VALUES"
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\&\fIEVP_PKEY_verify_recover_init()\fR and \fIEVP_PKEY_verify_recover()\fR return 1 for success
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and 0 or a negative value for failure. In particular a return value of \-2
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indicates the operation is not supported by the public key algorithm.
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.SH "EXAMPLE"
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.IX Header "EXAMPLE"
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Recover digest originally signed using PKCS#1 and \s-1SHA256\s0 digest:
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.PP
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.Vb 2
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\& #include <openssl/evp.h>
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\& #include <openssl/rsa.h>
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\&
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\& EVP_PKEY_CTX *ctx;
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\& unsigned char *rout, *sig;
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\& size_t routlen, siglen;
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\& EVP_PKEY *verify_key;
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\& /* NB: assumes verify_key, sig and siglen are already set up
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\& * and that verify_key is an RSA public key
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\& */
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\& ctx = EVP_PKEY_CTX_new(verify_key);
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\& if (!ctx)
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\& /* Error occurred */
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\& if (EVP_PKEY_verify_recover_init(ctx) <= 0)
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\& /* Error */
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\& if (EVP_PKEY_CTX_set_rsa_padding(ctx, RSA_PKCS1_PADDING) <= 0)
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\& /* Error */
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\& if (EVP_PKEY_CTX_set_signature_md(ctx, EVP_sha256()) <= 0)
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\& /* Error */
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\&
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\& /* Determine buffer length */
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\& if (EVP_PKEY_verify_recover(ctx, NULL, &routlen, sig, siglen) <= 0)
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\& /* Error */
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\&
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\& rout = OPENSSL_malloc(routlen);
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\&
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\& if (!rout)
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\& /* malloc failure */
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\&
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\& if (EVP_PKEY_verify_recover(ctx, rout, &routlen, sig, siglen) <= 0)
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\& /* Error */
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\&
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\& /* Recovered data is routlen bytes written to buffer rout */
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.Ve
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.SH "SEE ALSO"
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.IX Header "SEE ALSO"
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\&\fIEVP_PKEY_CTX_new\fR\|(3),
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\&\fIEVP_PKEY_encrypt\fR\|(3),
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\&\fIEVP_PKEY_decrypt\fR\|(3),
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\&\fIEVP_PKEY_sign\fR\|(3),
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\&\fIEVP_PKEY_verify\fR\|(3),
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\&\fIEVP_PKEY_derive\fR\|(3)
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.SH "HISTORY"
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.IX Header "HISTORY"
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These functions were first added to OpenSSL 1.0.0.
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