306 lines
13 KiB
Groff
Executable File
306 lines
13 KiB
Groff
Executable File
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.\" ========================================================================
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.\"
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.IX Title "EVP_DIGESTSIGNINIT 3"
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.TH EVP_DIGESTSIGNINIT 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_DigestSignInit_ex, EVP_DigestSignInit, EVP_DigestSignUpdate,
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EVP_DigestSignFinal, EVP_DigestSign \- 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_DigestSignInit_ex(EVP_MD_CTX *ctx, EVP_PKEY_CTX **pctx,
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\& const char *mdname, const char *props,
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\& EVP_PKEY *pkey);
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\& int EVP_DigestSignInit(EVP_MD_CTX *ctx, EVP_PKEY_CTX **pctx,
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\& const EVP_MD *type, ENGINE *e, EVP_PKEY *pkey);
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\& int EVP_DigestSignUpdate(EVP_MD_CTX *ctx, const void *d, size_t cnt);
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\& int EVP_DigestSignFinal(EVP_MD_CTX *ctx, unsigned char *sig, size_t *siglen);
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\&
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\& int EVP_DigestSign(EVP_MD_CTX *ctx, unsigned char *sigret,
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\& size_t *siglen, const unsigned char *tbs,
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\& size_t tbslen);
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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 signatures.
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Input data is digested first before the signing takes place.
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.PP
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\&\fIEVP_DigestSignInit_ex()\fR sets up signing context \fIctx\fR to use a digest with the
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name \fImdname\fR and private key \fIpkey\fR. The name of the digest to be used is
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passed to the provider of the signature algorithm in use. How that provider
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interprets the digest name is provider specific. The provider may implement
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that digest directly itself or it may (optionally) choose to fetch it (which
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could result in a digest from a different provider being selected). If the
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provider supports fetching the digest then it may use the \fIprops\fR argument for
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the properties to be used during the fetch.
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.PP
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The \fIpkey\fR algorithm is used to fetch a \fB\s-1EVP_SIGNATURE\s0\fR method implicitly, to
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be used for the actual signing. See \*(L"Implicit fetch\*(R" in \fIprovider\fR\|(7) for
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more information about implict fetches.
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.PP
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The OpenSSL default and legacy providers support fetching digests and can fetch
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those digests from any available provider. The OpenSSL fips provider also
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supports fetching digests but will only fetch digests that are themselves
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implemented inside the fips provider.
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.PP
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\&\fIctx\fR must be created with \fIEVP_MD_CTX_new()\fR before calling this function. If
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\&\fIpctx\fR is not \s-1NULL\s0, the \s-1EVP_PKEY_CTX\s0 of the signing operation will be written
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to \fI*pctx\fR: this can be used to set alternative signing options. Note that any
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existing value in \fI*pctx\fR is overwritten. The \s-1EVP_PKEY_CTX\s0 value returned must
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not be freed directly by the application if \fIctx\fR is not assigned an
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\&\s-1EVP_PKEY_CTX\s0 value before being passed to \fIEVP_DigestSignInit_ex()\fR (which means
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the \s-1EVP_PKEY_CTX\s0 is created inside \fIEVP_DigestSignInit_ex()\fR and it will be freed
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automatically when the \s-1EVP_MD_CTX\s0 is freed).
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.PP
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The digest \fImdname\fR may be \s-1NULL\s0 if the signing algorithm supports it. The
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\&\fIprops\fR argument can always be \s-1NULL\s0.
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.PP
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No \fB\s-1EVP_PKEY_CTX\s0\fR will be created by \fIEVP_DigestSignInit_ex()\fR if the passed
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\&\fIctx\fR has already been assigned one via \fIEVP_MD_CTX_set_pkey_ctx\fR\|(3). See also
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\&\s-1\fISM2\s0\fR\|(7).
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.PP
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Only \s-1EVP_PKEY\s0 types that support signing can be used with these functions. This
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includes \s-1MAC\s0 algorithms where the \s-1MAC\s0 generation is considered as a form of
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\&\*(L"signing\*(R". Built-in \s-1EVP_PKEY\s0 types supported by these functions are \s-1CMAC\s0,
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Poly1305, \s-1DSA\s0, \s-1ECDSA\s0, \s-1HMAC\s0, \s-1RSA\s0, SipHash, Ed25519 and Ed448.
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.PP
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Not all digests can be used for all key types. The following combinations apply.
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.IP "\s-1DSA\s0" 4
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.IX Item "DSA"
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Supports \s-1SHA1\s0, \s-1SHA224\s0, \s-1SHA256\s0, \s-1SHA384\s0 and \s-1SHA512\s0
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.IP "\s-1ECDSA\s0" 4
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.IX Item "ECDSA"
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Supports \s-1SHA1\s0, \s-1SHA224\s0, \s-1SHA256\s0, \s-1SHA384\s0, \s-1SHA512\s0 and \s-1SM3\s0
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.IP "\s-1RSA\s0 with no padding" 4
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.IX Item "RSA with no padding"
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Supports no digests (the digest \fItype\fR must be \s-1NULL\s0)
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.IP "\s-1RSA\s0 with X931 padding" 4
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.IX Item "RSA with X931 padding"
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Supports \s-1SHA1\s0, \s-1SHA256\s0, \s-1SHA384\s0 and \s-1SHA512\s0
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.IP "All other \s-1RSA\s0 padding types" 4
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.IX Item "All other RSA padding types"
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Support \s-1SHA1\s0, \s-1SHA224\s0, \s-1SHA256\s0, \s-1SHA384\s0, \s-1SHA512\s0, \s-1MD5\s0, \s-1MD5_SHA1\s0, \s-1MD2\s0, \s-1MD4\s0, \s-1MDC2\s0,
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\&\s-1SHA3\-224\s0, \s-1SHA3\-256\s0, \s-1SHA3\-384\s0, \s-1SHA3\-512\s0
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.IP "Ed25519 and Ed448" 4
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.IX Item "Ed25519 and Ed448"
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Support no digests (the digest \fItype\fR must be \s-1NULL\s0)
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.IP "\s-1HMAC\s0" 4
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.IX Item "HMAC"
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Supports any digest
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.IP "\s-1CMAC\s0, Poly1305 and SipHash" 4
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.IX Item "CMAC, Poly1305 and SipHash"
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Will ignore any digest provided.
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.PP
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If RSA-PSS is used and restrictions apply then the digest must match.
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.PP
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\&\fIEVP_DigestSignInit()\fR works in the same way as \fIEVP_DigestSignInit_ex()\fR except
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that the \fImdname\fR parameter will be inferred from the supplied digest \fItype\fR,
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and \fIprops\fR will be \s-1NULL\s0. Where supplied the \s-1ENGINE\s0 \fIe\fR will be used for the
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signing and digest algorithm implementations. \fIe\fR may be \s-1NULL\s0.
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.PP
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\&\fIEVP_DigestSignUpdate()\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_DigestSignFinal()\fR signs the data in \fIctx\fR and places the signature in \fIsig\fR.
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If \fIsig\fR is \s-1NULL\s0 then the maximum size of the output buffer is written to
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the \fIsiglen\fR parameter. If \fIsig\fR is not \s-1NULL\s0 then before the call the
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\&\fIsiglen\fR parameter should contain the length of the \fIsig\fR buffer. If the
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call is successful the signature is written to \fIsig\fR and the amount of data
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written to \fIsiglen\fR.
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.PP
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\&\fIEVP_DigestSign()\fR signs \fItbslen\fR bytes of data at \fItbs\fR and places the
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signature in \fIsig\fR and its length in \fIsiglen\fR in a similar way to
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\&\fIEVP_DigestSignFinal()\fR.
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.SH "RETURN VALUES"
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.IX Header "RETURN VALUES"
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\&\fIEVP_DigestSignInit()\fR, \fIEVP_DigestSignUpdate()\fR, \fIEVP_DigestSignFinal()\fR and
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\&\fIEVP_DigestSign()\fR return 1 for success and 0 for failure.
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.PP
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The error codes can be obtained from \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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\&\fIEVP_DigestSign()\fR is a one shot operation which signs a single block of data
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in one function. For algorithms that support streaming it is equivalent to
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calling \fIEVP_DigestSignUpdate()\fR and \fIEVP_DigestSignFinal()\fR. For algorithms which
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do not support streaming (e.g. PureEdDSA) it is the only way to sign data.
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.PP
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In previous versions of OpenSSL there was a link between message digest types
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and public key algorithms. This meant that \*(L"clone\*(R" digests such as \fIEVP_dss1()\fR
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needed to be used to sign using \s-1SHA1\s0 and \s-1DSA\s0. This is no longer necessary and
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the use of clone digest is now discouraged.
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.PP
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For some key types and parameters 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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.PP
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The call to \fIEVP_DigestSignFinal()\fR internally finalizes a copy of the digest
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context. This means that calls to \fIEVP_DigestSignUpdate()\fR and
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\&\fIEVP_DigestSignFinal()\fR can be called 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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.PP
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The use of \fIEVP_PKEY_size()\fR with these functions is discouraged because some
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signature operations may have a signature length which depends on the
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parameters set. As a result \fIEVP_PKEY_size()\fR would have to return a value
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which indicates the maximum possible signature for any set of parameters.
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.SH "SEE ALSO"
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.IX Header "SEE ALSO"
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\&\fIEVP_DigestVerifyInit\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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\&\s-1\fIRAND\s0\fR\|(7)
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.SH "HISTORY"
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.IX Header "HISTORY"
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\&\fIEVP_DigestSignInit()\fR, \fIEVP_DigestSignUpdate()\fR and \fIEVP_DigestSignFinal()\fR
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were added in OpenSSL 1.0.0.
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.PP
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\&\fIEVP_DigestSignInit_ex()\fR was added in OpenSSL 3.0.
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.PP
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\&\fIEVP_DigestSignUpdate()\fR was converted from a macro to a function in OpenSSL 3.0.
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.SH "COPYRIGHT"
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.IX Header "COPYRIGHT"
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Copyright 2006\-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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