1EVP_DIGESTSIGNINIT(3)               OpenSSL              EVP_DIGESTSIGNINIT(3)
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NAME

6       EVP_DigestSignInit, EVP_DigestSignUpdate, EVP_DigestSignFinal,
7       EVP_DigestSign - EVP signing functions
8

SYNOPSIS

10        #include <openssl/evp.h>
11
12        int EVP_DigestSignInit(EVP_MD_CTX *ctx, EVP_PKEY_CTX **pctx,
13                               const EVP_MD *type, ENGINE *e, EVP_PKEY *pkey);
14        int EVP_DigestSignUpdate(EVP_MD_CTX *ctx, const void *d, size_t cnt);
15        int EVP_DigestSignFinal(EVP_MD_CTX *ctx, unsigned char *sig, size_t *siglen);
16
17        int EVP_DigestSign(EVP_MD_CTX *ctx, unsigned char *sigret,
18                           size_t *siglen, const unsigned char *tbs,
19                           size_t tbslen);
20

DESCRIPTION

22       The EVP signature routines are a high level interface to digital
23       signatures.
24
25       EVP_DigestSignInit() sets up signing context ctx to use digest type
26       from ENGINE e and private key pkey. ctx must be created with
27       EVP_MD_CTX_new() before calling this function. If pctx is not NULL, the
28       EVP_PKEY_CTX of the signing operation will be written to *pctx: this
29       can be used to set alternative signing options. Note that any existing
30       value in *pctx is overwritten. The EVP_PKEY_CTX value returned must not
31       be freed directly by the application if ctx is not assigned an
32       EVP_PKEY_CTX value before being passed to EVP_DigestSignInit() (which
33       means the EVP_PKEY_CTX is created inside EVP_DigestSignInit() and it
34       will be freed automatically when the EVP_MD_CTX is freed).
35
36       The digest type may be NULL if the signing algorithm supports it.
37
38       No EVP_PKEY_CTX will be created by EVP_DigestSignInit() if the passed
39       ctx has already been assigned one via EVP_MD_CTX_set_ctx(3). See also
40       SM2(7).
41
42       Only EVP_PKEY types that support signing can be used with these
43       functions. This includes MAC algorithms where the MAC generation is
44       considered as a form of "signing". Built-in EVP_PKEY types supported by
45       these functions are CMAC, Poly1305, DSA, ECDSA, HMAC, RSA, SipHash,
46       Ed25519 and Ed448.
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48       Not all digests can be used for all key types. The following
49       combinations apply.
50
51       DSA Supports SHA1, SHA224, SHA256, SHA384 and SHA512
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53       ECDSA
54           Supports SHA1, SHA224, SHA256, SHA384, SHA512 and SM3
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56       RSA with no padding
57           Supports no digests (the digest type must be NULL)
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59       RSA with X931 padding
60           Supports SHA1, SHA256, SHA384 and SHA512
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62       All other RSA padding types
63           Support SHA1, SHA224, SHA256, SHA384, SHA512, MD5, MD5_SHA1, MD2,
64           MD4, MDC2, SHA3-224, SHA3-256, SHA3-384, SHA3-512
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66       Ed25519 and Ed448
67           Support no digests (the digest type must be NULL)
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69       HMAC
70           Supports any digest
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72       CMAC, Poly1305 and SipHash
73           Will ignore any digest provided.
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75       If RSA-PSS is used and restrictions apply then the digest must match.
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77       EVP_DigestSignUpdate() hashes cnt bytes of data at d into the signature
78       context ctx. This function can be called several times on the same ctx
79       to include additional data. This function is currently implemented
80       using a macro.
81
82       EVP_DigestSignFinal() signs the data in ctx and places the signature in
83       sig.  If sig is NULL then the maximum size of the output buffer is
84       written to the siglen parameter. If sig is not NULL then before the
85       call the siglen parameter should contain the length of the sig buffer.
86       If the call is successful the signature is written to sig and the
87       amount of data written to siglen.
88
89       EVP_DigestSign() signs tbslen bytes of data at tbs and places the
90       signature in sig and its length in siglen in a similar way to
91       EVP_DigestSignFinal().
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RETURN VALUES

94       EVP_DigestSignInit(), EVP_DigestSignUpdate(), EVP_DigestSignaFinal()
95       and EVP_DigestSign() return 1 for success and 0 or a negative value for
96       failure. In particular, a return value of -2 indicates the operation is
97       not supported by the public key algorithm.
98
99       The error codes can be obtained from ERR_get_error(3).
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NOTES

102       The EVP interface to digital signatures should almost always be used in
103       preference to the low level interfaces. This is because the code then
104       becomes transparent to the algorithm used and much more flexible.
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106       EVP_DigestSign() is a one shot operation which signs a single block of
107       data in one function. For algorithms that support streaming it is
108       equivalent to calling EVP_DigestSignUpdate() and EVP_DigestSignFinal().
109       For algorithms which do not support streaming (e.g. PureEdDSA) it is
110       the only way to sign data.
111
112       In previous versions of OpenSSL there was a link between message digest
113       types and public key algorithms. This meant that "clone" digests such
114       as EVP_dss1() needed to be used to sign using SHA1 and DSA. This is no
115       longer necessary and the use of clone digest is now discouraged.
116
117       For some key types and parameters the random number generator must be
118       seeded.  If the automatic seeding or reseeding of the OpenSSL CSPRNG
119       fails due to external circumstances (see RAND(7)), the operation will
120       fail.
121
122       The call to EVP_DigestSignFinal() internally finalizes a copy of the
123       digest context. This means that calls to EVP_DigestSignUpdate() and
124       EVP_DigestSignFinal() can be called later to digest and sign additional
125       data.
126
127       Since only a copy of the digest context is ever finalized, the context
128       must be cleaned up after use by calling EVP_MD_CTX_free() or a memory
129       leak will occur.
130
131       The use of EVP_PKEY_size() with these functions is discouraged because
132       some signature operations may have a signature length which depends on
133       the parameters set. As a result EVP_PKEY_size() would have to return a
134       value which indicates the maximum possible signature for any set of
135       parameters.
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SEE ALSO

138       EVP_DigestVerifyInit(3), EVP_DigestInit(3), evp(7), HMAC(3), MD2(3),
139       MD5(3), MDC2(3), RIPEMD160(3), SHA1(3), dgst(1), RAND(7)
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HISTORY

142       EVP_DigestSignInit(), EVP_DigestSignUpdate() and EVP_DigestSignFinal()
143       were added in OpenSSL 1.0.0.
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COPYRIGHT

146       Copyright 2006-2019 The OpenSSL Project Authors. All Rights Reserved.
147
148       Licensed under the OpenSSL license (the "License").  You may not use
149       this file except in compliance with the License.  You can obtain a copy
150       in the file LICENSE in the source distribution or at
151       <https://www.openssl.org/source/license.html>.
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1551.1.1d                            2019-10-03             EVP_DIGESTSIGNINIT(3)