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Editing: EVP_PKEY_verify_recover.3
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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 \- 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(EVP_PKEY_CTX *ctx, \& unsigned char *rout, size_t *routlen, \& const unsigned char *sig, size_t siglen); .Ve .SH "DESCRIPTION" .IX Header "DESCRIPTION" The \fBEVP_PKEY_verify_recover_init()\fR function initializes a public key algorithm context using key \fBpkey\fR for a verify recover operation. .PP The \fBEVP_PKEY_verify_recover()\fR function recovers signed data using \fBctx\fR. The signature is specified using the \fBsig\fR and \&\fBsiglen\fR parameters. If \fBrout\fR is \fB\s-1NULL\s0\fR then the maximum size of the output buffer is written to the \fBroutlen\fR parameter. If \fBrout\fR is not \fB\s-1NULL\s0\fR then before the call the \fBroutlen\fR parameter should contain the length of the \&\fBrout\fR buffer, if the call is successful recovered data is written to \&\fBrout\fR and the amount of data written to \fBroutlen\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 \s-1RSA\s0 in \s-1PKCS\s0 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 "EXAMPLE" .IX Header "EXAMPLE" Recover digest originally signed using PKCS#1 and \s-1SHA256\s0 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); \& 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" These functions were first added to OpenSSL 1.0.0.
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