1=pod
2
3=head1 NAME
4
5EVP_MD_CTX_init, EVP_MD_CTX_create, EVP_DigestInit_ex, EVP_DigestUpdate,
6EVP_DigestFinal_ex, EVP_MD_CTX_cleanup, EVP_MD_CTX_destroy, EVP_MAX_MD_SIZE,
7EVP_MD_CTX_copy_ex, EVP_MD_CTX_copy, EVP_MD_type, EVP_MD_pkey_type, EVP_MD_size,
8EVP_MD_block_size, EVP_MD_CTX_md, EVP_MD_CTX_size, EVP_MD_CTX_block_size, EVP_MD_CTX_type,
9EVP_md_null, EVP_md2, EVP_md5, EVP_sha, EVP_sha1, EVP_dss, EVP_dss1, EVP_mdc2,
10EVP_ripemd160, EVP_get_digestbyname, EVP_get_digestbynid, EVP_get_digestbyobj -
11EVP digest routines
12
13=head1 SYNOPSIS
14
15 #include <openssl/evp.h>
16
17 void EVP_MD_CTX_init(EVP_MD_CTX *ctx);
18 EVP_MD_CTX *EVP_MD_CTX_create(void);
19
20 int EVP_DigestInit_ex(EVP_MD_CTX *ctx, const EVP_MD *type, ENGINE *impl);
21 int EVP_DigestUpdate(EVP_MD_CTX *ctx, const void *d, size_t cnt);
22 int EVP_DigestFinal_ex(EVP_MD_CTX *ctx, unsigned char *md,
23        unsigned int *s);
24
25 int EVP_MD_CTX_cleanup(EVP_MD_CTX *ctx);
26 void EVP_MD_CTX_destroy(EVP_MD_CTX *ctx);
27
28 int EVP_MD_CTX_copy_ex(EVP_MD_CTX *out,const EVP_MD_CTX *in);  
29
30 int EVP_DigestInit(EVP_MD_CTX *ctx, const EVP_MD *type);
31 int EVP_DigestFinal(EVP_MD_CTX *ctx, unsigned char *md,
32        unsigned int *s);
33
34 int EVP_MD_CTX_copy(EVP_MD_CTX *out,EVP_MD_CTX *in);  
35
36 #define EVP_MAX_MD_SIZE (16+20) /* The SSLv3 md5+sha1 type */
37
38
39 #define EVP_MD_type(e)			((e)->type)
40 #define EVP_MD_pkey_type(e)		((e)->pkey_type)
41 #define EVP_MD_size(e)			((e)->md_size)
42 #define EVP_MD_block_size(e)		((e)->block_size)
43
44 #define EVP_MD_CTX_md(e)		(e)->digest)
45 #define EVP_MD_CTX_size(e)		EVP_MD_size((e)->digest)
46 #define EVP_MD_CTX_block_size(e)	EVP_MD_block_size((e)->digest)
47 #define EVP_MD_CTX_type(e)		EVP_MD_type((e)->digest)
48
49 const EVP_MD *EVP_md_null(void);
50 const EVP_MD *EVP_md2(void);
51 const EVP_MD *EVP_md5(void);
52 const EVP_MD *EVP_sha(void);
53 const EVP_MD *EVP_sha1(void);
54 const EVP_MD *EVP_dss(void);
55 const EVP_MD *EVP_dss1(void);
56 const EVP_MD *EVP_mdc2(void);
57 const EVP_MD *EVP_ripemd160(void);
58
59 const EVP_MD *EVP_get_digestbyname(const char *name);
60 #define EVP_get_digestbynid(a) EVP_get_digestbyname(OBJ_nid2sn(a))
61 #define EVP_get_digestbyobj(a) EVP_get_digestbynid(OBJ_obj2nid(a))
62
63=head1 DESCRIPTION
64
65The EVP digest routines are a high level interface to message digests.
66
67EVP_MD_CTX_init() initializes digest contet B<ctx>.
68
69EVP_MD_CTX_create() allocates, initializes and returns a digest contet.
70
71EVP_DigestInit_ex() sets up digest context B<ctx> to use a digest
72B<type> from ENGINE B<impl>. B<ctx> must be initialized before calling this
73function. B<type> will typically be supplied by a functionsuch as EVP_sha1().
74If B<impl> is NULL then the default implementation of digest B<type> is used.
75
76EVP_DigestUpdate() hashes B<cnt> bytes of data at B<d> into the
77digest context B<ctx>. This function can be called several times on the
78same B<ctx> to hash additional data.
79
80EVP_DigestFinal_ex() retrieves the digest value from B<ctx> and places
81it in B<md>. If the B<s> parameter is not NULL then the number of
82bytes of data written (i.e. the length of the digest) will be written
83to the integer at B<s>, at most B<EVP_MAX_MD_SIZE> bytes will be written.
84After calling EVP_DigestFinal_ex() no additional calls to EVP_DigestUpdate()
85can be made, but EVP_DigestInit_ex() can be called to initialize a new
86digest operation.
87
88EVP_MD_CTX_cleanup() cleans up digest context B<ctx>, it should be called
89after a digest context is no longer needed.
90
91EVP_MD_CTX_destroy() cleans up digest context B<ctx> and frees up the
92space allocated to it, it should be called only on a context created
93using EVP_MD_CTX_create().
94
95EVP_MD_CTX_copy_ex() can be used to copy the message digest state from
96B<in> to B<out>. This is useful if large amounts of data are to be
97hashed which only differ in the last few bytes. B<out> must be initialized
98before calling this function.
99
100EVP_DigestInit() behaves in the same way as EVP_DigestInit_ex() except
101the passed context B<ctx> does not have to be initialized, and it always
102uses the default digest implementation.
103
104EVP_DigestFinal() is similar to EVP_DigestFinal_ex() except the digest
105contet B<ctx> is automatically cleaned up.
106
107EVP_MD_CTX_copy() is similar to EVP_MD_CTX_copy_ex() except the destination
108B<out> does not have to be initialized.
109
110EVP_MD_size() and EVP_MD_CTX_size() return the size of the message digest
111when passed an B<EVP_MD> or an B<EVP_MD_CTX> structure, i.e. the size of the
112hash.
113
114EVP_MD_block_size() and EVP_MD_CTX_block_size() return the block size of the
115message digest when passed an B<EVP_MD> or an B<EVP_MD_CTX> structure.
116
117EVP_MD_type() and EVP_MD_CTX_type() return the NID of the OBJECT IDENTIFIER
118representing the given message digest when passed an B<EVP_MD> structure.
119For example EVP_MD_type(EVP_sha1()) returns B<NID_sha1>. This function is
120normally used when setting ASN1 OIDs.
121
122EVP_MD_CTX_md() returns the B<EVP_MD> structure corresponding to the passed
123B<EVP_MD_CTX>.
124
125EVP_MD_pkey_type() returns the NID of the public key signing algorithm associated
126with this digest. For example EVP_sha1() is associated with RSA so this will
127return B<NID_sha1WithRSAEncryption>. This "link" between digests and signature
128algorithms may not be retained in future versions of OpenSSL.
129
130EVP_md2(), EVP_md5(), EVP_sha(), EVP_sha1(), EVP_mdc2() and EVP_ripemd160()
131return B<EVP_MD> structures for the MD2, MD5, SHA, SHA1, MDC2 and RIPEMD160 digest
132algorithms respectively. The associated signature algorithm is RSA in each case.
133
134EVP_dss() and EVP_dss1() return B<EVP_MD> structures for SHA and SHA1 digest
135algorithms but using DSS (DSA) for the signature algorithm.
136
137EVP_md_null() is a "null" message digest that does nothing: i.e. the hash it
138returns is of zero length.
139
140EVP_get_digestbyname(), EVP_get_digestbynid() and EVP_get_digestbyobj()
141return an B<EVP_MD> structure when passed a digest name, a digest NID or
142an ASN1_OBJECT structure respectively. The digest table must be initialized
143using, for example, OpenSSL_add_all_digests() for these functions to work.
144
145=head1 RETURN VALUES
146
147EVP_DigestInit_ex(), EVP_DigestUpdate() and EVP_DigestFinal_ex() return 1 for
148success and 0 for failure.
149
150EVP_MD_CTX_copy_ex() returns 1 if successful or 0 for failure.
151
152EVP_MD_type(), EVP_MD_pkey_type() and EVP_MD_type() return the NID of the
153corresponding OBJECT IDENTIFIER or NID_undef if none exists.
154
155EVP_MD_size(), EVP_MD_block_size(), EVP_MD_CTX_size(e), EVP_MD_size(),
156EVP_MD_CTX_block_size()	and EVP_MD_block_size() return the digest or block
157size in bytes.
158
159EVP_md_null(), EVP_md2(), EVP_md5(), EVP_sha(), EVP_sha1(), EVP_dss(),
160EVP_dss1(), EVP_mdc2() and EVP_ripemd160() return pointers to the
161corresponding EVP_MD structures.
162
163EVP_get_digestbyname(), EVP_get_digestbynid() and EVP_get_digestbyobj()
164return either an B<EVP_MD> structure or NULL if an error occurs.
165
166=head1 NOTES
167
168The B<EVP> interface to message digests should almost always be used in
169preference to the low level interfaces. This is because the code then becomes
170transparent to the digest used and much more flexible.
171
172SHA1 is the digest of choice for new applications. The other digest algorithms
173are still in common use.
174
175For most applications the B<impl> parameter to EVP_DigestInit_ex() will be
176set to NULL to use the default digest implementation.
177
178The functions EVP_DigestInit(), EVP_DigestFinal() and EVP_MD_CTX_copy() are 
179obsolete but are retained to maintain compatibility with existing code. New
180applications should use EVP_DigestInit_ex(), EVP_DigestFinal_ex() and 
181EVP_MD_CTX_copy_ex() because they can efficiently reuse a digest context
182instead of initializing and cleaning it up on each call and allow non default
183implementations of digests to be specified.
184
185In OpenSSL 0.9.7 and later if digest contexts are not cleaned up after use
186memory leaks will occur. 
187
188=head1 EXAMPLE
189
190This example digests the data "Test Message\n" and "Hello World\n", using the
191digest name passed on the command line.
192
193 #include <stdio.h>
194 #include <openssl/evp.h>
195
196 main(int argc, char *argv[])
197 {
198 EVP_MD_CTX mdctx;
199 const EVP_MD *md;
200 char mess1[] = "Test Message\n";
201 char mess2[] = "Hello World\n";
202 unsigned char md_value[EVP_MAX_MD_SIZE];
203 int md_len, i;
204
205 OpenSSL_add_all_digests();
206
207 if(!argv[1]) {
208 	printf("Usage: mdtest digestname\n");
209	exit(1);
210 }
211
212 md = EVP_get_digestbyname(argv[1]);
213
214 if(!md) {
215 	printf("Unknown message digest %s\n", argv[1]);
216	exit(1);
217 }
218
219 EVP_MD_CTX_init(&mdctx);
220 EVP_DigestInit_ex(&mdctx, md, NULL);
221 EVP_DigestUpdate(&mdctx, mess1, strlen(mess1));
222 EVP_DigestUpdate(&mdctx, mess2, strlen(mess2));
223 EVP_DigestFinal_ex(&mdctx, md_value, &md_len);
224 EVP_MD_CTX_cleanup(&mdctx);
225
226 printf("Digest is: ");
227 for(i = 0; i < md_len; i++) printf("%02x", md_value[i]);
228 printf("\n");
229 }
230
231=head1 BUGS
232
233The link between digests and signing algorithms results in a situation where
234EVP_sha1() must be used with RSA and EVP_dss1() must be used with DSS
235even though they are identical digests.
236
237=head1 SEE ALSO
238
239L<evp(3)|evp(3)>, L<hmac(3)|hmac(3)>, L<md2(3)|md2(3)>,
240L<md5(3)|md5(3)>, L<mdc2(3)|mdc2(3)>, L<ripemd(3)|ripemd(3)>,
241L<sha(3)|sha(3)>, L<dgst(1)|dgst(1)>
242
243=head1 HISTORY
244
245EVP_DigestInit(), EVP_DigestUpdate() and EVP_DigestFinal() are
246available in all versions of SSLeay and OpenSSL.
247
248EVP_MD_CTX_init(), EVP_MD_CTX_create(), EVP_MD_CTX_copy_ex(),
249EVP_MD_CTX_cleanup(), EVP_MD_CTX_destroy(), EVP_DigestInit_ex()
250and EVP_DigestFinal_ex() were added in OpenSSL 0.9.7.
251
252EVP_md_null(), EVP_md2(), EVP_md5(), EVP_sha(), EVP_sha1(),
253EVP_dss(), EVP_dss1(), EVP_mdc2() and EVP_ripemd160() were
254changed to return truely const EVP_MD * in OpenSSL 0.9.7.
255
256=cut
257