EVP_MD_CTX_init(3ssl)

1EVP_DigestInit(3)                   OpenSSL                  EVP_DigestInit(3)
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NAME

6       EVP_MD_CTX_init, EVP_MD_CTX_create, EVP_DigestInit_ex,
7       EVP_DigestUpdate, EVP_DigestFinal_ex, EVP_MD_CTX_cleanup,
8       EVP_MD_CTX_destroy, EVP_MAX_MD_SIZE, EVP_MD_CTX_copy_ex,
9       EVP_MD_CTX_copy, EVP_MD_type, EVP_MD_pkey_type, EVP_MD_size,
10       EVP_MD_block_size, EVP_MD_CTX_md, EVP_MD_CTX_size,
11       EVP_MD_CTX_block_size, EVP_MD_CTX_type, EVP_md_null, EVP_md2, EVP_md5,
12       EVP_sha, EVP_sha1, EVP_sha224, EVP_sha256, EVP_sha384, EVP_sha512,
13       EVP_dss, EVP_dss1, EVP_mdc2, EVP_ripemd160, EVP_get_digestbyname,
14       EVP_get_digestbynid, EVP_get_digestbyobj - EVP digest routines
15

SYNOPSIS

17        #include <openssl/evp.h>
18
19        void EVP_MD_CTX_init(EVP_MD_CTX *ctx);
20        EVP_MD_CTX *EVP_MD_CTX_create(void);
21
22        int EVP_DigestInit_ex(EVP_MD_CTX *ctx, const EVP_MD *type, ENGINE *impl);
23        int EVP_DigestUpdate(EVP_MD_CTX *ctx, const void *d, size_t cnt);
24        int EVP_DigestFinal_ex(EVP_MD_CTX *ctx, unsigned char *md,
25               unsigned int *s);
26
27        int EVP_MD_CTX_cleanup(EVP_MD_CTX *ctx);
28        void EVP_MD_CTX_destroy(EVP_MD_CTX *ctx);
29
30        int EVP_MD_CTX_copy_ex(EVP_MD_CTX *out,const EVP_MD_CTX *in);
31
32        int EVP_DigestInit(EVP_MD_CTX *ctx, const EVP_MD *type);
33        int EVP_DigestFinal(EVP_MD_CTX *ctx, unsigned char *md,
34               unsigned int *s);
35
36        int EVP_MD_CTX_copy(EVP_MD_CTX *out,EVP_MD_CTX *in);
37
38        #define EVP_MAX_MD_SIZE 64     /* SHA512 */
39
40        int EVP_MD_type(const EVP_MD *md);
41        int EVP_MD_pkey_type(const EVP_MD *md);
42        int EVP_MD_size(const EVP_MD *md);
43        int EVP_MD_block_size(const EVP_MD *md);
44
45        const EVP_MD *EVP_MD_CTX_md(const EVP_MD_CTX *ctx);
46        #define EVP_MD_CTX_size(e)             EVP_MD_size(EVP_MD_CTX_md(e))
47        #define EVP_MD_CTX_block_size(e)       EVP_MD_block_size((e)->digest)
48        #define EVP_MD_CTX_type(e)             EVP_MD_type((e)->digest)
49
50        const EVP_MD *EVP_md_null(void);
51        const EVP_MD *EVP_md2(void);
52        const EVP_MD *EVP_md5(void);
53        const EVP_MD *EVP_sha(void);
54        const EVP_MD *EVP_sha1(void);
55        const EVP_MD *EVP_dss(void);
56        const EVP_MD *EVP_dss1(void);
57        const EVP_MD *EVP_mdc2(void);
58        const EVP_MD *EVP_ripemd160(void);
59
60        const EVP_MD *EVP_sha224(void);
61        const EVP_MD *EVP_sha256(void);
62        const EVP_MD *EVP_sha384(void);
63        const EVP_MD *EVP_sha512(void);
64
65        const EVP_MD *EVP_get_digestbyname(const char *name);
66        #define EVP_get_digestbynid(a) EVP_get_digestbyname(OBJ_nid2sn(a))
67        #define EVP_get_digestbyobj(a) EVP_get_digestbynid(OBJ_obj2nid(a))
68

DESCRIPTION

70       The EVP digest routines are a high level interface to message digests.
71
72       EVP_MD_CTX_init() initializes digest context ctx.
73
74       EVP_MD_CTX_create() allocates, initializes and returns a digest
75       context.
76
77       EVP_DigestInit_ex() sets up digest context ctx to use a digest type
78       from ENGINE impl. ctx must be initialized before calling this function.
79       type will typically be supplied by a function such as EVP_sha1().  If
80       impl is NULL then the default implementation of digest type is used.
81
82       EVP_DigestUpdate() hashes cnt bytes of data at d into the digest
83       context ctx. This function can be called several times on the same ctx
84       to hash additional data.
85
86       EVP_DigestFinal_ex() retrieves the digest value from ctx and places it
87       in md. If the s parameter is not NULL then the number of bytes of data
88       written (i.e. the length of the digest) will be written to the integer
89       at s, at most EVP_MAX_MD_SIZE bytes will be written.  After calling
90       EVP_DigestFinal_ex() no additional calls to EVP_DigestUpdate() can be
91       made, but EVP_DigestInit_ex() can be called to initialize a new digest
92       operation.
93
94       EVP_MD_CTX_cleanup() cleans up digest context ctx, it should be called
95       after a digest context is no longer needed.
96
97       EVP_MD_CTX_destroy() cleans up digest context ctx and frees up the
98       space allocated to it, it should be called only on a context created
99       using EVP_MD_CTX_create().
100
101       EVP_MD_CTX_copy_ex() can be used to copy the message digest state from
102       in to out. This is useful if large amounts of data are to be hashed
103       which only differ in the last few bytes. out must be initialized before
104       calling this function.
105
106       EVP_DigestInit() behaves in the same way as EVP_DigestInit_ex() except
107       the passed context ctx does not have to be initialized, and it always
108       uses the default digest implementation.
109
110       EVP_DigestFinal() is similar to EVP_DigestFinal_ex() except the digest
111       context ctx is automatically cleaned up.
112
113       EVP_MD_CTX_copy() is similar to EVP_MD_CTX_copy_ex() except the
114       destination out does not have to be initialized.
115
116       EVP_MD_size() and EVP_MD_CTX_size() return the size of the message
117       digest when passed an EVP_MD or an EVP_MD_CTX structure, i.e. the size
118       of the hash.
119
120       EVP_MD_block_size() and EVP_MD_CTX_block_size() return the block size
121       of the message digest when passed an EVP_MD or an EVP_MD_CTX structure.
122
123       EVP_MD_type() and EVP_MD_CTX_type() return the NID of the OBJECT
124       IDENTIFIER representing the given message digest when passed an EVP_MD
125       structure.  For example EVP_MD_type(EVP_sha1()) returns NID_sha1. This
126       function is normally used when setting ASN1 OIDs.
127
128       EVP_MD_CTX_md() returns the EVP_MD structure corresponding to the
129       passed EVP_MD_CTX.
130
131       EVP_MD_pkey_type() returns the NID of the public key signing algorithm
132       associated with this digest. For example EVP_sha1() is associated with
133       RSA so this will return NID_sha1WithRSAEncryption. Since digests and
134       signature algorithms are no longer linked this function is only
135       retained for compatibility reasons.
136
137       EVP_md2(), EVP_md5(), EVP_sha(), EVP_sha1(), EVP_sha224(),
138       EVP_sha256(), EVP_sha384(), EVP_sha512(), EVP_mdc2() and
139       EVP_ripemd160() return EVP_MD structures for the MD2, MD5, SHA, SHA1,
140       SHA224, SHA256, SHA384, SHA512, MDC2 and RIPEMD160 digest algorithms
141       respectively.
142
143       EVP_dss() and EVP_dss1() return EVP_MD structures for SHA and SHA1
144       digest algorithms but using DSS (DSA) for the signature algorithm.
145       Note: there is no need to use these pseudo-digests in OpenSSL 1.0.0 and
146       later, they are however retained for compatibility.
147
148       EVP_md_null() is a "null" message digest that does nothing: i.e. the
149       hash it returns is of zero length.
150
151       EVP_get_digestbyname(), EVP_get_digestbynid() and EVP_get_digestbyobj()
152       return an EVP_MD structure when passed a digest name, a digest NID or
153       an ASN1_OBJECT structure respectively. The digest table must be
154       initialized using, for example, OpenSSL_add_all_digests() for these
155       functions to work.
156

RETURN VALUES

158       EVP_DigestInit_ex(), EVP_DigestUpdate() and EVP_DigestFinal_ex() return
159       1 for success and 0 for failure.
160
161       EVP_MD_CTX_copy_ex() returns 1 if successful or 0 for failure.
162
163       EVP_MD_type(), EVP_MD_pkey_type() and EVP_MD_type() return the NID of
164       the corresponding OBJECT IDENTIFIER or NID_undef if none exists.
165
166       EVP_MD_size(), EVP_MD_block_size(), EVP_MD_CTX_size(e), EVP_MD_size(),
167       EVP_MD_CTX_block_size()  and EVP_MD_block_size() return the digest or
168       block size in bytes.
169
170       EVP_md_null(), EVP_md2(), EVP_md5(), EVP_sha(), EVP_sha1(),
171       EVP_sha224(), EVP_sha256(), EVP_sha384(), EVP_sha512(), EVP_dss(),
172       EVP_dss1(), EVP_mdc2() and EVP_ripemd160() return pointers to the
173       corresponding EVP_MD structures.
174
175       EVP_get_digestbyname(), EVP_get_digestbynid() and EVP_get_digestbyobj()
176       return either an EVP_MD structure or NULL if an error occurs.
177

NOTES

179       The EVP interface to message digests should almost always be used in
180       preference to the low level interfaces. This is because the code then
181       becomes transparent to the digest used and much more flexible.
182
183       New applications should use the SHA2 digest algorithms such as SHA256.
184       The other digest algorithms are still in common use.
185
186       For most applications the impl parameter to EVP_DigestInit_ex() will be
187       set to NULL to use the default digest implementation.
188
189       The functions EVP_DigestInit(), EVP_DigestFinal() and EVP_MD_CTX_copy()
190       are obsolete but are retained to maintain compatibility with existing
191       code. New applications should use EVP_DigestInit_ex(),
192       EVP_DigestFinal_ex() and EVP_MD_CTX_copy_ex() because they can
193       efficiently reuse a digest context instead of initializing and cleaning
194       it up on each call and allow non default implementations of digests to
195       be specified.
196
197       In OpenSSL 0.9.7 and later if digest contexts are not cleaned up after
198       use memory leaks will occur.
199
200       Stack allocation of EVP_MD_CTX structures is common, for example:
201
202        EVP_MD_CTX mctx;
203        EVP_MD_CTX_init(&mctx);
204
205       This will cause binary compatibility issues if the size of EVP_MD_CTX
206       structure changes (this will only happen with a major release of
207       OpenSSL).  Applications wishing to avoid this should use
208       EVP_MD_CTX_create() instead:
209
210        EVP_MD_CTX *mctx;
211        mctx = EVP_MD_CTX_create();
212

EXAMPLE

214       This example digests the data "Test Message\n" and "Hello World\n",
215       using the digest name passed on the command line.
216
217        #include <stdio.h>
218        #include <openssl/evp.h>
219
220        main(int argc, char *argv[])
221        {
222        EVP_MD_CTX *mdctx;
223        const EVP_MD *md;
224        char mess1[] = "Test Message\n";
225        char mess2[] = "Hello World\n";
226        unsigned char md_value[EVP_MAX_MD_SIZE];
227        int md_len, i;
228
229        OpenSSL_add_all_digests();
230
231        if(!argv[1]) {
232               printf("Usage: mdtest digestname\n");
233               exit(1);
234        }
235
236        md = EVP_get_digestbyname(argv[1]);
237
238        if(!md) {
239               printf("Unknown message digest %s\n", argv[1]);
240               exit(1);
241        }
242
243        mdctx = EVP_MD_CTX_create();
244        EVP_DigestInit_ex(mdctx, md, NULL);
245        EVP_DigestUpdate(mdctx, mess1, strlen(mess1));
246        EVP_DigestUpdate(mdctx, mess2, strlen(mess2));
247        EVP_DigestFinal_ex(mdctx, md_value, &md_len);
248        EVP_MD_CTX_destroy(mdctx);
249
250        printf("Digest is: ");
251        for(i = 0; i < md_len; i++) printf("%02x", md_value[i]);
252        printf("\n");
253        }
254

HISTORY

259       EVP_DigestInit(), EVP_DigestUpdate() and EVP_DigestFinal() are
260       available in all versions of SSLeay and OpenSSL.
261
262       EVP_MD_CTX_init(), EVP_MD_CTX_create(), EVP_MD_CTX_copy_ex(),
263       EVP_MD_CTX_cleanup(), EVP_MD_CTX_destroy(), EVP_DigestInit_ex() and
264       EVP_DigestFinal_ex() were added in OpenSSL 0.9.7.
265
266       EVP_md_null(), EVP_md2(), EVP_md5(), EVP_sha(), EVP_sha1(), EVP_dss(),
267       EVP_dss1(), EVP_mdc2() and EVP_ripemd160() were changed to return
268       truely const EVP_MD * in OpenSSL 0.9.7.
269
270       The link between digests and signing algorithms was fixed in OpenSSL
271       1.0 and later, so now EVP_sha1() can be used with RSA and DSA, there is
272       no need to use EVP_dss1() any more.
273
274       OpenSSL 1.0 and later does not include the MD2 digest algorithm in the
275       default configuration due to its security weaknesses.
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2791.0.1e                            2017-03-22                 EVP_DigestInit(3)