1EVP_DIGESTINIT(3)                   OpenSSL                  EVP_DIGESTINIT(3)
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3
4

NAME

6       EVP_MD_CTX_new, EVP_MD_CTX_reset, EVP_MD_CTX_free, EVP_MD_CTX_copy,
7       EVP_MD_CTX_copy_ex, EVP_MD_CTX_ctrl, EVP_MD_CTX_set_flags,
8       EVP_MD_CTX_clear_flags, EVP_MD_CTX_test_flags, EVP_Digest,
9       EVP_DigestInit_ex, EVP_DigestInit, EVP_DigestUpdate,
10       EVP_DigestFinal_ex, EVP_DigestFinalXOF, EVP_DigestFinal, EVP_MD_type,
11       EVP_MD_pkey_type, EVP_MD_size, EVP_MD_block_size, EVP_MD_flags,
12       EVP_MD_CTX_md, EVP_MD_CTX_type, EVP_MD_CTX_size, EVP_MD_CTX_block_size,
13       EVP_MD_CTX_md_data, EVP_MD_CTX_update_fn, EVP_MD_CTX_set_update_fn,
14       EVP_md_null, EVP_get_digestbyname, EVP_get_digestbynid,
15       EVP_get_digestbyobj, EVP_MD_CTX_pkey_ctx, EVP_MD_CTX_set_pkey_ctx - EVP
16       digest routines
17

SYNOPSIS

19        #include <openssl/evp.h>
20
21        EVP_MD_CTX *EVP_MD_CTX_new(void);
22        int EVP_MD_CTX_reset(EVP_MD_CTX *ctx);
23        void EVP_MD_CTX_free(EVP_MD_CTX *ctx);
24        void EVP_MD_CTX_ctrl(EVP_MD_CTX *ctx, int cmd, int p1, void* p2);
25        void EVP_MD_CTX_set_flags(EVP_MD_CTX *ctx, int flags);
26        void EVP_MD_CTX_clear_flags(EVP_MD_CTX *ctx, int flags);
27        int EVP_MD_CTX_test_flags(const EVP_MD_CTX *ctx, int flags);
28
29        int EVP_Digest(const void *data, size_t count, unsigned char *md,
30                       unsigned int *size, const EVP_MD *type, ENGINE *impl);
31        int EVP_DigestInit_ex(EVP_MD_CTX *ctx, const EVP_MD *type, ENGINE *impl);
32        int EVP_DigestUpdate(EVP_MD_CTX *ctx, const void *d, size_t cnt);
33        int EVP_DigestFinal_ex(EVP_MD_CTX *ctx, unsigned char *md, unsigned int *s);
34        int EVP_DigestFinalXOF(EVP_MD_CTX *ctx, unsigned char *md, size_t len);
35
36        int EVP_MD_CTX_copy_ex(EVP_MD_CTX *out, const EVP_MD_CTX *in);
37
38        int EVP_DigestInit(EVP_MD_CTX *ctx, const EVP_MD *type);
39        int EVP_DigestFinal(EVP_MD_CTX *ctx, unsigned char *md, unsigned int *s);
40
41        int EVP_MD_CTX_copy(EVP_MD_CTX *out, EVP_MD_CTX *in);
42
43        int EVP_MD_type(const EVP_MD *md);
44        int EVP_MD_pkey_type(const EVP_MD *md);
45        int EVP_MD_size(const EVP_MD *md);
46        int EVP_MD_block_size(const EVP_MD *md);
47        unsigned long EVP_MD_flags(const EVP_MD *md);
48
49        const EVP_MD *EVP_MD_CTX_md(const EVP_MD_CTX *ctx);
50        int EVP_MD_CTX_size(const EVP_MD_CTX *ctx);
51        int EVP_MD_CTX_block_size(const EVP_MD_CTX *ctx);
52        int EVP_MD_CTX_type(const EVP_MD_CTX *ctx);
53        void *EVP_MD_CTX_md_data(const EVP_MD_CTX *ctx);
54        int (*EVP_MD_CTX_update_fn(EVP_MD_CTX *ctx))(EVP_MD_CTX *ctx,
55                                                     const void *data, size_t count);
56        void EVP_MD_CTX_set_update_fn(EVP_MD_CTX *ctx,
57                                      int (*update)(EVP_MD_CTX *ctx,
58                                                    const void *data, size_t count));
59
60        const EVP_MD *EVP_md_null(void);
61
62        const EVP_MD *EVP_get_digestbyname(const char *name);
63        const EVP_MD *EVP_get_digestbynid(int type);
64        const EVP_MD *EVP_get_digestbyobj(const ASN1_OBJECT *o);
65
66        EVP_PKEY_CTX *EVP_MD_CTX_pkey_ctx(const EVP_MD_CTX *ctx);
67        void EVP_MD_CTX_set_pkey_ctx(EVP_MD_CTX *ctx, EVP_PKEY_CTX *pctx);
68

DESCRIPTION

70       The EVP digest routines are a high-level interface to message digests,
71       and should be used instead of the cipher-specific functions.
72
73       EVP_MD_CTX_new()
74           Allocates and returns a digest context.
75
76       EVP_MD_CTX_reset()
77           Resets the digest context ctx.  This can be used to reuse an
78           already existing context.
79
80       EVP_MD_CTX_free()
81           Cleans up digest context ctx and frees up the space allocated to
82           it.
83
84       EVP_MD_CTX_ctrl()
85           Performs digest-specific control actions on context ctx. The
86           control command is indicated in cmd and any additional arguments in
87           p1 and p2.  EVP_MD_CTX_ctrl() must be called after
88           EVP_DigestInit_ex(). Other restrictions may apply depending on the
89           control type and digest implementation.  See "CONTROLS" below for
90           more information.
91
92       EVP_MD_CTX_set_flags(), EVP_MD_CTX_clear_flags(),
93       EVP_MD_CTX_test_flags()
94           Sets, clears and tests ctx flags.  See "FLAGS" below for more
95           information.
96
97       EVP_Digest()
98           A wrapper around the Digest Init_ex, Update and Final_ex functions.
99           Hashes count bytes of data at data using a digest type from ENGINE
100           impl. The digest value is placed in md and its length is written at
101           size if the pointer is not NULL. At most EVP_MAX_MD_SIZE bytes will
102           be written.  If impl is NULL the default implementation of digest
103           type is used.
104
105       EVP_DigestInit_ex()
106           Sets up digest context ctx to use a digest type from ENGINE impl.
107           type will typically be supplied by a function such as EVP_sha1().
108           If impl is NULL then the default implementation of digest type is
109           used.
110
111       EVP_DigestUpdate()
112           Hashes cnt bytes of data at d into the digest context ctx. This
113           function can be called several times on the same ctx to hash
114           additional data.
115
116       EVP_DigestFinal_ex()
117           Retrieves the digest value from ctx and places it in md. If the s
118           parameter is not NULL then the number of bytes of data written
119           (i.e. the length of the digest) will be written to the integer at
120           s, at most EVP_MAX_MD_SIZE bytes will be written.  After calling
121           EVP_DigestFinal_ex() no additional calls to EVP_DigestUpdate() can
122           be made, but EVP_DigestInit_ex() can be called to initialize a new
123           digest operation.
124
125       EVP_DigestFinalXOF()
126           Interfaces to extendable-output functions, XOFs, such as SHAKE128
127           and SHAKE256.  It retrieves the digest value from ctx and places it
128           in len-sized <B>md.  After calling this function no additional
129           calls to EVP_DigestUpdate() can be made, but EVP_DigestInit_ex()
130           can be called to initialize a new operation.
131
132       EVP_MD_CTX_copy_ex()
133           Can be used to copy the message digest state from in to out. This
134           is useful if large amounts of data are to be hashed which only
135           differ in the last few bytes.
136
137       EVP_DigestInit()
138           Behaves in the same way as EVP_DigestInit_ex() except it always
139           uses the default digest implementation and calls
140           EVP_MD_CTX_reset().
141
142       EVP_DigestFinal()
143           Similar to EVP_DigestFinal_ex() except the digest context ctx is
144           automatically cleaned up.
145
146       EVP_MD_CTX_copy()
147           Similar to EVP_MD_CTX_copy_ex() except the destination out does not
148           have to be initialized.
149
150       EVP_MD_size(), EVP_MD_CTX_size()
151           Return the size of the message digest when passed an EVP_MD or an
152           EVP_MD_CTX structure, i.e. the size of the hash.
153
154       EVP_MD_block_size(), EVP_MD_CTX_block_size()
155           Return the block size of the message digest when passed an EVP_MD
156           or an EVP_MD_CTX structure.
157
158       EVP_MD_type(), EVP_MD_CTX_type()
159           Return the NID of the OBJECT IDENTIFIER representing the given
160           message digest when passed an EVP_MD structure.  For example,
161           "EVP_MD_type(EVP_sha1())" returns NID_sha1. This function is
162           normally used when setting ASN1 OIDs.
163
164       EVP_MD_CTX_md_data()
165           Return the digest method private data for the passed EVP_MD_CTX.
166           The space is allocated by OpenSSL and has the size originally set
167           with EVP_MD_meth_set_app_datasize().
168
169       EVP_MD_CTX_md()
170           Returns the EVP_MD structure corresponding to the passed
171           EVP_MD_CTX.
172
173       EVP_MD_CTX_set_update_fn()
174           Sets the update function for ctx to update.  This is the function
175           that is called by EVP_DigestUpdate. If not set, the update function
176           from the EVP_MD type specified at initialization is used.
177
178       EVP_MD_CTX_update_fn()
179           Returns the update function for ctx.
180
181       EVP_MD_flags()
182           Returns the md flags. Note that these are different from the
183           EVP_MD_CTX ones. See EVP_MD_meth_set_flags(3) for more information.
184
185       EVP_MD_pkey_type()
186           Returns the NID of the public key signing algorithm associated with
187           this digest. For example EVP_sha1() is associated with RSA so this
188           will return NID_sha1WithRSAEncryption. Since digests and signature
189           algorithms are no longer linked this function is only retained for
190           compatibility reasons.
191
192       EVP_md_null()
193           A "null" message digest that does nothing: i.e. the hash it returns
194           is of zero length.
195
196       EVP_get_digestbyname(), EVP_get_digestbynid(), EVP_get_digestbyobj()
197           Returns an EVP_MD structure when passed a digest name, a digest NID
198           or an ASN1_OBJECT structure respectively.
199
200       EVP_MD_CTX_pkey_ctx()
201           Returns the EVP_PKEY_CTX assigned to ctx. The returned pointer
202           should not be freed by the caller.
203
204       EVP_MD_CTX_set_pkey_ctx()
205           Assigns an EVP_PKEY_CTX to EVP_MD_CTX. This is usually used to
206           provide a customized EVP_PKEY_CTX to EVP_DigestSignInit(3) or
207           EVP_DigestVerifyInit(3). The pctx passed to this function should be
208           freed by the caller. A NULL pctx pointer is also allowed to clear
209           the EVP_PKEY_CTX assigned to ctx. In such case, freeing the cleared
210           EVP_PKEY_CTX or not depends on how the EVP_PKEY_CTX is created.
211

CONTROLS

213       EVP_MD_CTX_ctrl() can be used to send the following standard controls:
214
215       EVP_MD_CTRL_MICALG
216           Gets the digest Message Integrity Check algorithm string. This is
217           used when creating S/MIME multipart/signed messages, as specified
218           in RFC 3851.  The string value is written to p2.
219
220       EVP_MD_CTRL_XOF_LEN
221           This control sets the digest length for extendable output functions
222           to p1.  Sending this control directly should not be necessary, the
223           use of "EVP_DigestFinalXOF()" is preferred.  Currently used by
224           SHAKE.
225

FLAGS

227       EVP_MD_CTX_set_flags(), EVP_MD_CTX_clear_flags() and
228       EVP_MD_CTX_test_flags() can be used the manipulate and test these
229       EVP_MD_CTX flags:
230
231       EVP_MD_CTX_FLAG_ONESHOT
232           This flag instructs the digest to optimize for one update only, if
233           possible.
234
235       EVP_MD_CTX_FLAG_NO_INIT
236           This flag instructs EVP_DigestInit() and similar not to initialise
237           the implementation specific data.
238
239       EVP_MD_CTX_FLAG_FINALISE
240           Some functions such as EVP_DigestSign only finalise copies of
241           internal contexts so additional data can be included after the
242           finalisation call.  This is inefficient if this functionality is
243           not required, and can be disabled with this flag.
244

RETURN VALUES

246       EVP_DigestInit_ex(), EVP_DigestUpdate(), EVP_DigestFinal_ex()
247           Returns 1 for success and 0 for failure.
248
249       EVP_MD_CTX_ctrl()
250           Returns 1 if successful or 0 for failure.
251
252       EVP_MD_CTX_copy_ex()
253           Returns 1 if successful or 0 for failure.
254
255       EVP_MD_type(), EVP_MD_pkey_type()
256           Returns the NID of the corresponding OBJECT IDENTIFIER or NID_undef
257           if none exists.
258
259       EVP_MD_size(), EVP_MD_block_size(), EVP_MD_CTX_size(),
260       EVP_MD_CTX_block_size()
261           Returns the digest or block size in bytes.
262
263       EVP_md_null()
264           Returns a pointer to the EVP_MD structure of the "null" message
265           digest.
266
267       EVP_get_digestbyname(), EVP_get_digestbynid(), EVP_get_digestbyobj()
268           Returns either an EVP_MD structure or NULL if an error occurs.
269
270       EVP_MD_CTX_set_pkey_ctx()
271           This function has no return value.
272

NOTES

274       The EVP interface to message digests should almost always be used in
275       preference to the low-level interfaces. This is because the code then
276       becomes transparent to the digest used and much more flexible.
277
278       New applications should use the SHA-2 (such as EVP_sha256(3)) or the
279       SHA-3 digest algorithms (such as EVP_sha3_512(3)). The other digest
280       algorithms are still in common use.
281
282       For most applications the impl parameter to EVP_DigestInit_ex() will be
283       set to NULL to use the default digest implementation.
284
285       The functions EVP_DigestInit(), EVP_DigestFinal() and EVP_MD_CTX_copy()
286       are obsolete but are retained to maintain compatibility with existing
287       code. New applications should use EVP_DigestInit_ex(),
288       EVP_DigestFinal_ex() and EVP_MD_CTX_copy_ex() because they can
289       efficiently reuse a digest context instead of initializing and cleaning
290       it up on each call and allow non default implementations of digests to
291       be specified.
292
293       If digest contexts are not cleaned up after use, memory leaks will
294       occur.
295
296       EVP_MD_CTX_size(), EVP_MD_CTX_block_size(), EVP_MD_CTX_type(),
297       EVP_get_digestbynid() and EVP_get_digestbyobj() are defined as macros.
298
299       EVP_MD_CTX_ctrl() sends commands to message digests for additional
300       configuration or control.
301

EXAMPLES

303       This example digests the data "Test Message\n" and "Hello World\n",
304       using the digest name passed on the command line.
305
306        #include <stdio.h>
307        #include <string.h>
308        #include <openssl/evp.h>
309
310        int main(int argc, char *argv[])
311        {
312            EVP_MD_CTX *mdctx;
313            const EVP_MD *md;
314            char mess1[] = "Test Message\n";
315            char mess2[] = "Hello World\n";
316            unsigned char md_value[EVP_MAX_MD_SIZE];
317            unsigned int md_len, i;
318
319            if (argv[1] == NULL) {
320                printf("Usage: mdtest digestname\n");
321                exit(1);
322            }
323
324            md = EVP_get_digestbyname(argv[1]);
325            if (md == NULL) {
326                printf("Unknown message digest %s\n", argv[1]);
327                exit(1);
328            }
329
330            mdctx = EVP_MD_CTX_new();
331            EVP_DigestInit_ex(mdctx, md, NULL);
332            EVP_DigestUpdate(mdctx, mess1, strlen(mess1));
333            EVP_DigestUpdate(mdctx, mess2, strlen(mess2));
334            EVP_DigestFinal_ex(mdctx, md_value, &md_len);
335            EVP_MD_CTX_free(mdctx);
336
337            printf("Digest is: ");
338            for (i = 0; i < md_len; i++)
339                printf("%02x", md_value[i]);
340            printf("\n");
341
342            exit(0);
343        }
344

SEE ALSO

346       EVP_MD_meth_new(3), dgst(1), evp(7)
347
348       The full list of digest algorithms are provided below.
349
350       EVP_blake2b512(3), EVP_md2(3), EVP_md4(3), EVP_md5(3), EVP_mdc2(3),
351       EVP_ripemd160(3), EVP_sha1(3), EVP_sha224(3), EVP_sha3_224(3),
352       EVP_sm3(3), EVP_whirlpool(3)
353

HISTORY

355       The EVP_MD_CTX_create() and EVP_MD_CTX_destroy() functions were renamed
356       to EVP_MD_CTX_new() and EVP_MD_CTX_free() in OpenSSL 1.1.0,
357       respectively.
358
359       The link between digests and signing algorithms was fixed in OpenSSL
360       1.0 and later, so now EVP_sha1() can be used with RSA and DSA.
361
362       The EVP_dss1() function was removed in OpenSSL 1.1.0.
363
364       The EVP_MD_CTX_set_pkey_ctx() function was added in 1.1.1.
365
367       Copyright 2000-2020 The OpenSSL Project Authors. All Rights Reserved.
368
369       Licensed under the OpenSSL license (the "License").  You may not use
370       this file except in compliance with the License.  You can obtain a copy
371       in the file LICENSE in the source distribution or at
372       <https://www.openssl.org/source/license.html>.
373
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375
3761.1.1k                            2021-03-26                 EVP_DIGESTINIT(3)
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