221 lines
7.7 KiB
Groff
Executable File
221 lines
7.7 KiB
Groff
Executable File
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.\" ========================================================================
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.\"
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.IX Title "EVP_SIGNINIT 3"
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.TH EVP_SIGNINIT 3 "2020-03-02" "3.0.0-dev" "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_SignInit, EVP_SignInit_ex, EVP_SignUpdate, EVP_SignFinal
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\&\- EVP signing functions
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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_SignInit_ex(EVP_MD_CTX *ctx, const EVP_MD *type, ENGINE *impl);
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\& int EVP_SignUpdate(EVP_MD_CTX *ctx, const void *d, unsigned int cnt);
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\& int EVP_SignFinal(EVP_MD_CTX *ctx, unsigned char *sig, unsigned int *s, EVP_PKEY *pkey);
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\&
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\& void EVP_SignInit(EVP_MD_CTX *ctx, const EVP_MD *type);
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.Ve
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.SH "DESCRIPTION"
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.IX Header "DESCRIPTION"
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The \s-1EVP\s0 signature routines are a high level interface to digital
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signatures.
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.PP
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\&\fIEVP_SignInit_ex()\fR sets up signing context \fIctx\fR to use digest
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\&\fItype\fR from \fB\s-1ENGINE\s0\fR \fIimpl\fR. \fIctx\fR must be created with
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\&\fIEVP_MD_CTX_new()\fR before calling this function.
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.PP
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\&\fIEVP_SignUpdate()\fR hashes \fIcnt\fR bytes of data at \fId\fR into the
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signature context \fIctx\fR. This function can be called several times on the
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same \fIctx\fR to include additional data.
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.PP
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\&\fIEVP_SignFinal()\fR signs the data in \fIctx\fR using the private key \fIpkey\fR and
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places the signature in \fIsig\fR. \fIsig\fR must be at least \f(CW\*(C`EVP_PKEY_size(pkey)\*(C'\fR
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bytes in size. \fIs\fR is an \s-1OUT\s0 parameter, and not used as an \s-1IN\s0 parameter.
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The number of bytes of data written (i.e. the length of the signature)
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will be written to the integer at \fIs\fR, at most \f(CW\*(C`EVP_PKEY_size(pkey)\*(C'\fR bytes
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will be written.
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.PP
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\&\fIEVP_SignInit()\fR initializes a signing context \fIctx\fR to use the default
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implementation of digest \fItype\fR.
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.SH "RETURN VALUES"
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.IX Header "RETURN VALUES"
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\&\fIEVP_SignInit_ex()\fR, \fIEVP_SignUpdate()\fR and \fIEVP_SignFinal()\fR return 1
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for success and 0 for failure.
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.PP
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The error codes can be obtained by \fIERR_get_error\fR\|(3).
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.SH "NOTES"
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.IX Header "NOTES"
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The \fB\s-1EVP\s0\fR interface to digital signatures should almost always be used in
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preference to the low level interfaces. This is because the code then becomes
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transparent to the algorithm used and much more flexible.
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.PP
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When signing with \s-1DSA\s0 private keys the random number generator must be seeded.
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If the automatic seeding or reseeding of the OpenSSL \s-1CSPRNG\s0 fails due to
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external circumstances (see \s-1\fIRAND\s0\fR\|(7)), the operation will fail.
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This requirement does not hold for \s-1RSA\s0 signatures.
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.PP
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The call to \fIEVP_SignFinal()\fR internally finalizes a copy of the digest context.
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This means that calls to \fIEVP_SignUpdate()\fR and \fIEVP_SignFinal()\fR can be called
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later to digest and sign additional data.
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.PP
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Since only a copy of the digest context is ever finalized the context must
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be cleaned up after use by calling \fIEVP_MD_CTX_free()\fR or a memory leak
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will occur.
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.SH "BUGS"
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.IX Header "BUGS"
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Older versions of this documentation wrongly stated that calls to
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\&\fIEVP_SignUpdate()\fR could not be made after calling \fIEVP_SignFinal()\fR.
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.PP
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Since the private key is passed in the call to \fIEVP_SignFinal()\fR any error
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relating to the private key (for example an unsuitable key and digest
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combination) will not be indicated until after potentially large amounts of
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data have been passed through \fIEVP_SignUpdate()\fR.
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.PP
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It is not possible to change the signing parameters using these function.
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.PP
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The previous two bugs are fixed in the newer EVP_SignDigest*() function.
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.SH "SEE ALSO"
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.IX Header "SEE ALSO"
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\&\fIEVP_PKEY_size\fR\|(3), \fIEVP_PKEY_bits\fR\|(3), \fIEVP_PKEY_security_bits\fR\|(3),
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\&\fIEVP_VerifyInit\fR\|(3),
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\&\fIEVP_DigestInit\fR\|(3),
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\&\fIevp\fR\|(7), \s-1\fIHMAC\s0\fR\|(3), \s-1\fIMD2\s0\fR\|(3),
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\&\s-1\fIMD5\s0\fR\|(3), \s-1\fIMDC2\s0\fR\|(3), \s-1\fIRIPEMD160\s0\fR\|(3),
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\&\s-1\fISHA1\s0\fR\|(3), \fIopenssl\-dgst\fR\|(1)
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.SH "COPYRIGHT"
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.IX Header "COPYRIGHT"
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Copyright 2000\-2018 The OpenSSL Project Authors. All Rights Reserved.
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.PP
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Licensed under the Apache License 2.0 (the \*(L"License\*(R"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file \s-1LICENSE\s0 in the source distribution or at
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<https://www.openssl.org/source/license.html>.
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