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124.\" ========================================================================
125.\"
126.IX Title "EVP_DigestInit 3"
127.TH EVP_DigestInit 3 "2010-06-01" "1.0.0a" "OpenSSL"
128.\" For nroff, turn off justification. Always turn off hyphenation; it makes
129.\" way too many mistakes in technical documents.
130.if n .ad l
131.nh
132.SH "NAME"
133EVP_MD_CTX_init, EVP_MD_CTX_create, EVP_DigestInit_ex, EVP_DigestUpdate,
134EVP_DigestFinal_ex, EVP_MD_CTX_cleanup, EVP_MD_CTX_destroy, EVP_MAX_MD_SIZE,
135EVP_MD_CTX_copy_ex, EVP_MD_CTX_copy, EVP_MD_type, EVP_MD_pkey_type, EVP_MD_size,
136EVP_MD_block_size, EVP_MD_CTX_md, EVP_MD_CTX_size, EVP_MD_CTX_block_size, EVP_MD_CTX_type,
137EVP_md_null, EVP_md2, EVP_md5, EVP_sha, EVP_sha1, EVP_dss, EVP_dss1, EVP_mdc2,
138EVP_ripemd160, EVP_get_digestbyname, EVP_get_digestbynid, EVP_get_digestbyobj \-
139EVP digest routines
140.SH "SYNOPSIS"
141.IX Header "SYNOPSIS"
142.Vb 1
143\& #include <openssl/evp.h>
144\&
145\& void EVP_MD_CTX_init(EVP_MD_CTX *ctx);
146\& EVP_MD_CTX *EVP_MD_CTX_create(void);
147\&
148\& int EVP_DigestInit_ex(EVP_MD_CTX *ctx, const EVP_MD *type, ENGINE *impl);
149\& int EVP_DigestUpdate(EVP_MD_CTX *ctx, const void *d, size_t cnt);
150\& int EVP_DigestFinal_ex(EVP_MD_CTX *ctx, unsigned char *md,
151\& unsigned int *s);
152\&
153\& int EVP_MD_CTX_cleanup(EVP_MD_CTX *ctx);
154\& void EVP_MD_CTX_destroy(EVP_MD_CTX *ctx);
155\&
156\& int EVP_MD_CTX_copy_ex(EVP_MD_CTX *out,const EVP_MD_CTX *in);
157\&
158\& int EVP_DigestInit(EVP_MD_CTX *ctx, const EVP_MD *type);
159\& int EVP_DigestFinal(EVP_MD_CTX *ctx, unsigned char *md,
160\& unsigned int *s);
161\&
162\& int EVP_MD_CTX_copy(EVP_MD_CTX *out,EVP_MD_CTX *in);
163\&
164\& #define EVP_MAX_MD_SIZE (16+20) /* The SSLv3 md5+sha1 type */
165\&
166\&
167\& #define EVP_MD_type(e) ((e)\->type)
168\& #define EVP_MD_pkey_type(e) ((e)\->pkey_type)
169\& #define EVP_MD_size(e) ((e)\->md_size)
170\& #define EVP_MD_block_size(e) ((e)\->block_size)
171\&
172\& #define EVP_MD_CTX_md(e) (e)\->digest)
173\& #define EVP_MD_CTX_size(e) EVP_MD_size((e)\->digest)
174\& #define EVP_MD_CTX_block_size(e) EVP_MD_block_size((e)\->digest)
175\& #define EVP_MD_CTX_type(e) EVP_MD_type((e)\->digest)
176\&
177\& const EVP_MD *EVP_md_null(void);
178\& const EVP_MD *EVP_md2(void);
179\& const EVP_MD *EVP_md5(void);
180\& const EVP_MD *EVP_sha(void);
181\& const EVP_MD *EVP_sha1(void);
182\& const EVP_MD *EVP_dss(void);
183\& const EVP_MD *EVP_dss1(void);
184\& const EVP_MD *EVP_mdc2(void);
185\& const EVP_MD *EVP_ripemd160(void);
186\&
187\& const EVP_MD *EVP_get_digestbyname(const char *name);
188\& #define EVP_get_digestbynid(a) EVP_get_digestbyname(OBJ_nid2sn(a))
189\& #define EVP_get_digestbyobj(a) EVP_get_digestbynid(OBJ_obj2nid(a))
190.Ve
191.SH "DESCRIPTION"
192.IX Header "DESCRIPTION"
193The \s-1EVP\s0 digest routines are a high level interface to message digests.
194.PP
195\&\fIEVP_MD_CTX_init()\fR initializes digest context \fBctx\fR.
196.PP
197\&\fIEVP_MD_CTX_create()\fR allocates, initializes and returns a digest context.
198.PP
199\&\fIEVP_DigestInit_ex()\fR sets up digest context \fBctx\fR to use a digest
200\&\fBtype\fR from \s-1ENGINE\s0 \fBimpl\fR. \fBctx\fR must be initialized before calling this
201function. \fBtype\fR will typically be supplied by a functionsuch as \fIEVP_sha1()\fR.
202If \fBimpl\fR is \s-1NULL\s0 then the default implementation of digest \fBtype\fR is used.
203.PP
204\&\fIEVP_DigestUpdate()\fR hashes \fBcnt\fR bytes of data at \fBd\fR into the
205digest context \fBctx\fR. This function can be called several times on the
206same \fBctx\fR to hash additional data.
207.PP
208\&\fIEVP_DigestFinal_ex()\fR retrieves the digest value from \fBctx\fR and places
209it in \fBmd\fR. If the \fBs\fR parameter is not \s-1NULL\s0 then the number of
210bytes of data written (i.e. the length of the digest) will be written
211to the integer at \fBs\fR, at most \fB\s-1EVP_MAX_MD_SIZE\s0\fR bytes will be written.
212After calling \fIEVP_DigestFinal_ex()\fR no additional calls to \fIEVP_DigestUpdate()\fR
213can be made, but \fIEVP_DigestInit_ex()\fR can be called to initialize a new
214digest operation.
215.PP
216\&\fIEVP_MD_CTX_cleanup()\fR cleans up digest context \fBctx\fR, it should be called
217after a digest context is no longer needed.
218.PP
219\&\fIEVP_MD_CTX_destroy()\fR cleans up digest context \fBctx\fR and frees up the
220space allocated to it, it should be called only on a context created
221using \fIEVP_MD_CTX_create()\fR.
222.PP
223\&\fIEVP_MD_CTX_copy_ex()\fR can be used to copy the message digest state from
224\&\fBin\fR to \fBout\fR. This is useful if large amounts of data are to be
225hashed which only differ in the last few bytes. \fBout\fR must be initialized
226before calling this function.
227.PP
228\&\fIEVP_DigestInit()\fR behaves in the same way as \fIEVP_DigestInit_ex()\fR except
229the passed context \fBctx\fR does not have to be initialized, and it always
230uses the default digest implementation.
231.PP
232\&\fIEVP_DigestFinal()\fR is similar to \fIEVP_DigestFinal_ex()\fR except the digest
233context \fBctx\fR is automatically cleaned up.
234.PP
235\&\fIEVP_MD_CTX_copy()\fR is similar to \fIEVP_MD_CTX_copy_ex()\fR except the destination
236\&\fBout\fR does not have to be initialized.
237.PP
238\&\fIEVP_MD_size()\fR and \fIEVP_MD_CTX_size()\fR return the size of the message digest
239when passed an \fB\s-1EVP_MD\s0\fR or an \fB\s-1EVP_MD_CTX\s0\fR structure, i.e. the size of the
240hash.
241.PP
242\&\fIEVP_MD_block_size()\fR and \fIEVP_MD_CTX_block_size()\fR return the block size of the
243message digest when passed an \fB\s-1EVP_MD\s0\fR or an \fB\s-1EVP_MD_CTX\s0\fR structure.
244.PP
245\&\fIEVP_MD_type()\fR and \fIEVP_MD_CTX_type()\fR return the \s-1NID\s0 of the \s-1OBJECT\s0 \s-1IDENTIFIER\s0
246representing the given message digest when passed an \fB\s-1EVP_MD\s0\fR structure.
247For example EVP_MD_type(\fIEVP_sha1()\fR) returns \fBNID_sha1\fR. This function is
248normally used when setting \s-1ASN1\s0 OIDs.
249.PP
250\&\fIEVP_MD_CTX_md()\fR returns the \fB\s-1EVP_MD\s0\fR structure corresponding to the passed
251\&\fB\s-1EVP_MD_CTX\s0\fR.
252.PP
253\&\fIEVP_MD_pkey_type()\fR returns the \s-1NID\s0 of the public key signing algorithm associated
254with this digest. For example \fIEVP_sha1()\fR is associated with \s-1RSA\s0 so this will
255return \fBNID_sha1WithRSAEncryption\fR. This \*(L"link\*(R" between digests and signature
256algorithms may not be retained in future versions of OpenSSL.
257.PP
258\&\fIEVP_md2()\fR, \fIEVP_md5()\fR, \fIEVP_sha()\fR, \fIEVP_sha1()\fR, \fIEVP_mdc2()\fR and \fIEVP_ripemd160()\fR
259return \fB\s-1EVP_MD\s0\fR structures for the \s-1MD2\s0, \s-1MD5\s0, \s-1SHA\s0, \s-1SHA1\s0, \s-1MDC2\s0 and \s-1RIPEMD160\s0 digest
260algorithms respectively. The associated signature algorithm is \s-1RSA\s0 in each case.
261.PP
262\&\fIEVP_dss()\fR and \fIEVP_dss1()\fR return \fB\s-1EVP_MD\s0\fR structures for \s-1SHA\s0 and \s-1SHA1\s0 digest
263algorithms but using \s-1DSS\s0 (\s-1DSA\s0) for the signature algorithm. Note: there is
264no need to use these pseudo-digests in OpenSSL 1.0.0 and later, they are
265however retained for compatibility.
266.PP
267\&\fIEVP_md_null()\fR is a \*(L"null\*(R" message digest that does nothing: i.e. the hash it
268returns is of zero length.
269.PP
270\&\fIEVP_get_digestbyname()\fR, \fIEVP_get_digestbynid()\fR and \fIEVP_get_digestbyobj()\fR
271return an \fB\s-1EVP_MD\s0\fR structure when passed a digest name, a digest \s-1NID\s0 or
272an \s-1ASN1_OBJECT\s0 structure respectively. The digest table must be initialized
273using, for example, \fIOpenSSL_add_all_digests()\fR for these functions to work.
274.SH "RETURN VALUES"
275.IX Header "RETURN VALUES"
276\&\fIEVP_DigestInit_ex()\fR, \fIEVP_DigestUpdate()\fR and \fIEVP_DigestFinal_ex()\fR return 1 for
277success and 0 for failure.
278.PP
279\&\fIEVP_MD_CTX_copy_ex()\fR returns 1 if successful or 0 for failure.
280.PP
281\&\fIEVP_MD_type()\fR, \fIEVP_MD_pkey_type()\fR and \fIEVP_MD_type()\fR return the \s-1NID\s0 of the
282corresponding \s-1OBJECT\s0 \s-1IDENTIFIER\s0 or NID_undef if none exists.
283.PP
284\&\fIEVP_MD_size()\fR, \fIEVP_MD_block_size()\fR, EVP_MD_CTX_size(e), \fIEVP_MD_size()\fR,
285\&\fIEVP_MD_CTX_block_size()\fR and \fIEVP_MD_block_size()\fR return the digest or block
286size in bytes.
287.PP
288\&\fIEVP_md_null()\fR, \fIEVP_md2()\fR, \fIEVP_md5()\fR, \fIEVP_sha()\fR, \fIEVP_sha1()\fR, \fIEVP_dss()\fR,
289\&\fIEVP_dss1()\fR, \fIEVP_mdc2()\fR and \fIEVP_ripemd160()\fR return pointers to the
290corresponding \s-1EVP_MD\s0 structures.
291.PP
292\&\fIEVP_get_digestbyname()\fR, \fIEVP_get_digestbynid()\fR and \fIEVP_get_digestbyobj()\fR
293return either an \fB\s-1EVP_MD\s0\fR structure or \s-1NULL\s0 if an error occurs.
294.SH "NOTES"
295.IX Header "NOTES"
296The \fB\s-1EVP\s0\fR interface to message digests should almost always be used in
297preference to the low level interfaces. This is because the code then becomes
298transparent to the digest used and much more flexible.
299.PP
300\&\s-1SHA1\s0 is the digest of choice for new applications. The other digest algorithms
301are still in common use.
302.PP
303For most applications the \fBimpl\fR parameter to \fIEVP_DigestInit_ex()\fR will be
304set to \s-1NULL\s0 to use the default digest implementation.
305.PP
306The functions \fIEVP_DigestInit()\fR, \fIEVP_DigestFinal()\fR and \fIEVP_MD_CTX_copy()\fR are
307obsolete but are retained to maintain compatibility with existing code. New
308applications should use \fIEVP_DigestInit_ex()\fR, \fIEVP_DigestFinal_ex()\fR and
309\&\fIEVP_MD_CTX_copy_ex()\fR because they can efficiently reuse a digest context
310instead of initializing and cleaning it up on each call and allow non default
311implementations of digests to be specified.
312.PP
313In OpenSSL 0.9.7 and later if digest contexts are not cleaned up after use
314memory leaks will occur.
315.SH "EXAMPLE"
316.IX Header "EXAMPLE"
317This example digests the data \*(L"Test Message\en\*(R" and \*(L"Hello World\en\*(R", using the
318digest name passed on the command line.
319.PP
320.Vb 2
321\& #include <stdio.h>
322\& #include <openssl/evp.h>
323\&
324\& main(int argc, char *argv[])
325\& {
326\& EVP_MD_CTX mdctx;
327\& const EVP_MD *md;
328\& char mess1[] = "Test Message\en";
329\& char mess2[] = "Hello World\en";
330\& unsigned char md_value[EVP_MAX_MD_SIZE];
331\& int md_len, i;
332\&
333\& OpenSSL_add_all_digests();
334\&
335\& if(!argv[1]) {
336\& printf("Usage: mdtest digestname\en");
337\& exit(1);
338\& }
339\&
340\& md = EVP_get_digestbyname(argv[1]);
341\&
342\& if(!md) {
343\& printf("Unknown message digest %s\en", argv[1]);
344\& exit(1);
345\& }
346\&
347\& EVP_MD_CTX_init(&mdctx);
348\& EVP_DigestInit_ex(&mdctx, md, NULL);
349\& EVP_DigestUpdate(&mdctx, mess1, strlen(mess1));
350\& EVP_DigestUpdate(&mdctx, mess2, strlen(mess2));
351\& EVP_DigestFinal_ex(&mdctx, md_value, &md_len);
352\& EVP_MD_CTX_cleanup(&mdctx);
353\&
354\& printf("Digest is: ");
355\& for(i = 0; i < md_len; i++) printf("%02x", md_value[i]);
356\& printf("\en");
357\& }
358.Ve
359.SH "SEE ALSO"
360.IX Header "SEE ALSO"
361\&\fIevp\fR\|(3), \fIhmac\fR\|(3), \fImd2\fR\|(3),
362\&\fImd5\fR\|(3), \fImdc2\fR\|(3), \fIripemd\fR\|(3),
363\&\fIsha\fR\|(3), \fIdgst\fR\|(1)
364.SH "HISTORY"
365.IX Header "HISTORY"
366\&\fIEVP_DigestInit()\fR, \fIEVP_DigestUpdate()\fR and \fIEVP_DigestFinal()\fR are
367available in all versions of SSLeay and OpenSSL.
368.PP
369\&\fIEVP_MD_CTX_init()\fR, \fIEVP_MD_CTX_create()\fR, \fIEVP_MD_CTX_copy_ex()\fR,
370\&\fIEVP_MD_CTX_cleanup()\fR, \fIEVP_MD_CTX_destroy()\fR, \fIEVP_DigestInit_ex()\fR
371and \fIEVP_DigestFinal_ex()\fR were added in OpenSSL 0.9.7.
372.PP
373\&\fIEVP_md_null()\fR, \fIEVP_md2()\fR, \fIEVP_md5()\fR, \fIEVP_sha()\fR, \fIEVP_sha1()\fR,
374\&\fIEVP_dss()\fR, \fIEVP_dss1()\fR, \fIEVP_mdc2()\fR and \fIEVP_ripemd160()\fR were
375changed to return truely const \s-1EVP_MD\s0 * in OpenSSL 0.9.7.
376.PP
377The link between digests and signing algorithms was fixed in OpenSSL 1.0 and
378later, so now \fIEVP_sha1()\fR can be used with \s-1RSA\s0 and \s-1DSA\s0, there is no need to
379use \fIEVP_dss1()\fR any more.
380.PP
381OpenSSL 1.0 and later does not include the \s-1MD2\s0 digest algorithm in the
382default configuration due to its security weaknesses.