1EVP_SIGNINIT(3)                     OpenSSL                    EVP_SIGNINIT(3)
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NAME

6       EVP_SignInit, EVP_SignInit_ex, EVP_SignUpdate, EVP_SignFinal - EVP
7       signing functions
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SYNOPSIS

10        #include <openssl/evp.h>
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12        int EVP_SignInit_ex(EVP_MD_CTX *ctx, const EVP_MD *type, ENGINE *impl);
13        int EVP_SignUpdate(EVP_MD_CTX *ctx, const void *d, unsigned int cnt);
14        int EVP_SignFinal(EVP_MD_CTX *ctx, unsigned char *sig, unsigned int *s, EVP_PKEY *pkey);
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16        void EVP_SignInit(EVP_MD_CTX *ctx, const EVP_MD *type);
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DESCRIPTION

19       The EVP signature routines are a high-level interface to digital
20       signatures.
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22       EVP_SignInit_ex() sets up signing context ctx to use digest type from
23       ENGINE impl. ctx must be created with EVP_MD_CTX_new() before calling
24       this function.
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26       EVP_SignUpdate() hashes cnt bytes of data at d into the signature
27       context ctx. This function can be called several times on the same ctx
28       to include additional data.
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30       EVP_SignFinal() signs the data in ctx using the private key pkey and
31       places the signature in sig. sig must be at least EVP_PKEY_size(pkey)
32       bytes in size. s is an OUT parameter, and not used as an IN parameter.
33       The number of bytes of data written (i.e. the length of the signature)
34       will be written to the integer at s, at most EVP_PKEY_size(pkey) bytes
35       will be written.
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37       EVP_SignInit() initializes a signing context ctx to use the default
38       implementation of digest type.
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RETURN VALUES

41       EVP_SignInit_ex(), EVP_SignUpdate() and EVP_SignFinal() return 1 for
42       success and 0 for failure.
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44       The error codes can be obtained by ERR_get_error(3).
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NOTES

47       The EVP interface to digital signatures should almost always be used in
48       preference to the low-level interfaces. This is because the code then
49       becomes transparent to the algorithm used and much more flexible.
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51       When signing with DSA private keys the random number generator must be
52       seeded.  If the automatic seeding or reseeding of the OpenSSL CSPRNG
53       fails due to external circumstances (see RAND(7)), the operation will
54       fail.  This requirement does not hold for RSA signatures.
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56       The call to EVP_SignFinal() internally finalizes a copy of the digest
57       context.  This means that calls to EVP_SignUpdate() and EVP_SignFinal()
58       can be called later to digest and sign additional data.
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60       Since only a copy of the digest context is ever finalized the context
61       must be cleaned up after use by calling EVP_MD_CTX_free() or a memory
62       leak will occur.
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BUGS

65       Older versions of this documentation wrongly stated that calls to
66       EVP_SignUpdate() could not be made after calling EVP_SignFinal().
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68       Since the private key is passed in the call to EVP_SignFinal() any
69       error relating to the private key (for example an unsuitable key and
70       digest combination) will not be indicated until after potentially large
71       amounts of data have been passed through EVP_SignUpdate().
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73       It is not possible to change the signing parameters using these
74       function.
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76       The previous two bugs are fixed in the newer EVP_SignDigest*()
77       function.
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SEE ALSO

80       EVP_PKEY_size(3), EVP_PKEY_bits(3), EVP_PKEY_security_bits(3),
81       EVP_VerifyInit(3), EVP_DigestInit(3), evp(7), HMAC(3), MD2(3), MD5(3),
82       MDC2(3), RIPEMD160(3), SHA1(3), dgst(1)
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85       Copyright 2000-2020 The OpenSSL Project Authors. All Rights Reserved.
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87       Licensed under the OpenSSL license (the "License").  You may not use
88       this file except in compliance with the License.  You can obtain a copy
89       in the file LICENSE in the source distribution or at
90       <https://www.openssl.org/source/license.html>.
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941.1.1q                            2023-02-06                   EVP_SIGNINIT(3)
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