NAME¶
EVP_MD_CTX_init, EVP_MD_CTX_create, EVP_DigestInit_ex, EVP_DigestUpdate,
EVP_DigestFinal_ex, EVP_MD_CTX_cleanup, EVP_MD_CTX_destroy, EVP_MAX_MD_SIZE,
EVP_MD_CTX_copy_ex, EVP_MD_CTX_copy, EVP_MD_type, EVP_MD_pkey_type,
EVP_MD_size, EVP_MD_block_size, EVP_MD_CTX_md, EVP_MD_CTX_size,
EVP_MD_CTX_block_size, EVP_MD_CTX_type, EVP_md_null, EVP_md2, EVP_md5,
EVP_sha, EVP_sha1, EVP_sha224, EVP_sha256, EVP_sha384, EVP_sha512, EVP_dss,
EVP_dss1, EVP_mdc2, EVP_ripemd160, EVP_get_digestbyname, EVP_get_digestbynid,
EVP_get_digestbyobj - EVP digest routines
SYNOPSIS¶
#include <openssl/evp.h>
void EVP_MD_CTX_init(EVP_MD_CTX *ctx);
EVP_MD_CTX *EVP_MD_CTX_create(void);
int EVP_DigestInit_ex(EVP_MD_CTX *ctx, const EVP_MD *type, ENGINE *impl);
int EVP_DigestUpdate(EVP_MD_CTX *ctx, const void *d, size_t cnt);
int EVP_DigestFinal_ex(EVP_MD_CTX *ctx, unsigned char *md,
unsigned int *s);
int EVP_MD_CTX_cleanup(EVP_MD_CTX *ctx);
void EVP_MD_CTX_destroy(EVP_MD_CTX *ctx);
int EVP_MD_CTX_copy_ex(EVP_MD_CTX *out,const EVP_MD_CTX *in);
int EVP_DigestInit(EVP_MD_CTX *ctx, const EVP_MD *type);
int EVP_DigestFinal(EVP_MD_CTX *ctx, unsigned char *md,
unsigned int *s);
int EVP_MD_CTX_copy(EVP_MD_CTX *out,EVP_MD_CTX *in);
#define EVP_MAX_MD_SIZE 64 /* SHA512 */
int EVP_MD_type(const EVP_MD *md);
int EVP_MD_pkey_type(const EVP_MD *md);
int EVP_MD_size(const EVP_MD *md);
int EVP_MD_block_size(const EVP_MD *md);
const EVP_MD *EVP_MD_CTX_md(const EVP_MD_CTX *ctx);
#define EVP_MD_CTX_size(e) EVP_MD_size(EVP_MD_CTX_md(e))
#define EVP_MD_CTX_block_size(e) EVP_MD_block_size((e)->digest)
#define EVP_MD_CTX_type(e) EVP_MD_type((e)->digest)
const EVP_MD *EVP_md_null(void);
const EVP_MD *EVP_md2(void);
const EVP_MD *EVP_md5(void);
const EVP_MD *EVP_sha(void);
const EVP_MD *EVP_sha1(void);
const EVP_MD *EVP_dss(void);
const EVP_MD *EVP_dss1(void);
const EVP_MD *EVP_mdc2(void);
const EVP_MD *EVP_ripemd160(void);
const EVP_MD *EVP_sha224(void);
const EVP_MD *EVP_sha256(void);
const EVP_MD *EVP_sha384(void);
const EVP_MD *EVP_sha512(void);
const EVP_MD *EVP_get_digestbyname(const char *name);
#define EVP_get_digestbynid(a) EVP_get_digestbyname(OBJ_nid2sn(a))
#define EVP_get_digestbyobj(a) EVP_get_digestbynid(OBJ_obj2nid(a))
DESCRIPTION¶
The EVP digest routines are a high level interface to message digests.
EVP_MD_CTX_init() initializes digest context
ctx.
EVP_MD_CTX_create() allocates, initializes and returns a digest context.
EVP_DigestInit_ex() sets up digest context
ctx to use a digest
type from ENGINE
impl.
ctx must be initialized before
calling this function.
type will typically be supplied by a
functionsuch as
EVP_sha1(). If
impl is NULL then the default
implementation of digest
type is used.
EVP_DigestUpdate() hashes
cnt bytes of data at
d into the
digest context
ctx. This function can be called several times on the
same
ctx to hash additional data.
EVP_DigestFinal_ex() retrieves the digest value from
ctx and
places it in
md. If the
s parameter is not NULL then the number
of bytes of data written (i.e. the length of the digest) will be written to
the integer at
s, at most
EVP_MAX_MD_SIZE bytes will be written.
After calling
EVP_DigestFinal_ex() no additional calls to
EVP_DigestUpdate() can be made, but
EVP_DigestInit_ex() can be
called to initialize a new digest operation.
EVP_MD_CTX_cleanup() cleans up digest context
ctx, it should be
called after a digest context is no longer needed.
EVP_MD_CTX_destroy() cleans up digest context
ctx and frees up the
space allocated to it, it should be called only on a context created using
EVP_MD_CTX_create().
EVP_MD_CTX_copy_ex() can be used to copy the message digest state from
in to
out. This is useful if large amounts of data are to be
hashed which only differ in the last few bytes.
out must be initialized
before calling this function.
EVP_DigestInit() behaves in the same way as
EVP_DigestInit_ex()
except the passed context
ctx does not have to be initialized, and it
always uses the default digest implementation.
EVP_DigestFinal() is similar to
EVP_DigestFinal_ex() except the
digest context
ctx is automatically cleaned up.
EVP_MD_CTX_copy() is similar to
EVP_MD_CTX_copy_ex() except the
destination
out does not have to be initialized.
EVP_MD_size() and
EVP_MD_CTX_size() return the size of the message
digest when passed an
EVP_MD or an
EVP_MD_CTX structure, i.e.
the size of the hash.
EVP_MD_block_size() and
EVP_MD_CTX_block_size() return the block
size of the message digest when passed an
EVP_MD or an
EVP_MD_CTX structure.
EVP_MD_type() and
EVP_MD_CTX_type() return the NID of the OBJECT
IDENTIFIER representing the given message digest when passed an
EVP_MD
structure. For example EVP_MD_type(
EVP_sha1()) returns
NID_sha1. This function is normally used when setting ASN1 OIDs.
EVP_MD_CTX_md() returns the
EVP_MD structure corresponding to the
passed
EVP_MD_CTX.
EVP_MD_pkey_type() returns the NID of the public key signing algorithm
associated with this digest. For example
EVP_sha1() is associated with
RSA so this will return
NID_sha1WithRSAEncryption. Since digests and
signature algorithms are no longer linked this function is only retained for
compatibility reasons.
EVP_md2(),
EVP_md5(),
EVP_sha(),
EVP_sha1(),
EVP_sha224(),
EVP_sha256(),
EVP_sha384(),
EVP_sha512(),
EVP_mdc2() and
EVP_ripemd160() return
EVP_MD structures for the MD2, MD5, SHA, SHA1, SHA224, SHA256, SHA384,
SHA512, MDC2 and RIPEMD160 digest algorithms respectively.
EVP_dss() and
EVP_dss1() return
EVP_MD structures for SHA
and SHA1 digest algorithms but using DSS (DSA) for the signature algorithm.
Note: there is no need to use these pseudo-digests in OpenSSL 1.0.0 and later,
they are however retained for compatibility.
EVP_md_null() is a "null" message digest that does nothing:
i.e. the hash it returns is of zero length.
EVP_get_digestbyname(),
EVP_get_digestbynid() and
EVP_get_digestbyobj() return an
EVP_MD structure when passed a
digest name, a digest NID or an ASN1_OBJECT structure respectively. The digest
table must be initialized using, for example,
OpenSSL_add_all_digests()
for these functions to work.
RETURN VALUES¶
EVP_DigestInit_ex(),
EVP_DigestUpdate() and
EVP_DigestFinal_ex() return 1 for success and 0 for failure.
EVP_MD_CTX_copy_ex() returns 1 if successful or 0 for failure.
EVP_MD_type(),
EVP_MD_pkey_type() and
EVP_MD_type() return
the NID of the corresponding OBJECT IDENTIFIER or NID_undef if none exists.
EVP_MD_size(),
EVP_MD_block_size(),
EVP_MD_CTX_size() and
EVP_MD_CTX_block_size() return the digest or block size in bytes.
EVP_md_null(),
EVP_md2(),
EVP_md5(),
EVP_sha(),
EVP_sha1(),
EVP_dss(),
EVP_dss1(),
EVP_mdc2() and
EVP_ripemd160() return pointers to the corresponding EVP_MD structures.
EVP_get_digestbyname(),
EVP_get_digestbynid() and
EVP_get_digestbyobj() return either an
EVP_MD structure or NULL
if an error occurs.
NOTES¶
The
EVP interface to message digests should almost always be used in
preference to the low level interfaces. This is because the code then becomes
transparent to the digest used and much more flexible.
New applications should use the SHA2 digest algorithms such as SHA256. The other
digest algorithms are still in common use.
For most applications the
impl parameter to
EVP_DigestInit_ex()
will be set to NULL to use the default digest implementation.
The functions
EVP_DigestInit(),
EVP_DigestFinal() and
EVP_MD_CTX_copy() are obsolete but are retained to maintain
compatibility with existing code. New applications should use
EVP_DigestInit_ex(),
EVP_DigestFinal_ex() and
EVP_MD_CTX_copy_ex() because they can efficiently reuse a digest
context instead of initializing and cleaning it up on each call and allow non
default implementations of digests to be specified.
In OpenSSL 0.9.7 and later if digest contexts are not cleaned up after use
memory leaks will occur.
Stack allocation of EVP_MD_CTX structures is common, for example:
EVP_MD_CTX mctx;
EVP_MD_CTX_init(&mctx);
This will cause binary compatibility issues if the size of EVP_MD_CTX structure
changes (this will only happen with a major release of OpenSSL). Applications
wishing to avoid this should use
EVP_MD_CTX_create() instead:
EVP_MD_CTX *mctx;
mctx = EVP_MD_CTX_create();
EXAMPLE¶
This example digests the data "Test Message\n" and "Hello
World\n", using the digest name passed on the command line.
#include <stdio.h>
#include <openssl/evp.h>
main(int argc, char *argv[])
{
EVP_MD_CTX *mdctx;
const EVP_MD *md;
char mess1[] = "Test Message\n";
char mess2[] = "Hello World\n";
unsigned char md_value[EVP_MAX_MD_SIZE];
int md_len, i;
OpenSSL_add_all_digests();
if(!argv[1]) {
printf("Usage: mdtest digestname\n");
exit(1);
}
md = EVP_get_digestbyname(argv[1]);
if(!md) {
printf("Unknown message digest %s\n", argv[1]);
exit(1);
}
mdctx = EVP_MD_CTX_create();
EVP_DigestInit_ex(mdctx, md, NULL);
EVP_DigestUpdate(mdctx, mess1, strlen(mess1));
EVP_DigestUpdate(mdctx, mess2, strlen(mess2));
EVP_DigestFinal_ex(mdctx, md_value, &md_len);
EVP_MD_CTX_destroy(mdctx);
printf("Digest is: ");
for(i = 0; i < md_len; i++)
printf("%02x", md_value[i]);
printf("\n");
/* Call this once before exit. */
EVP_cleanup();
exit(0);
}
SEE ALSO¶
dgst(1),
evp(3)
HISTORY¶
EVP_DigestInit(),
EVP_DigestUpdate() and
EVP_DigestFinal()
are available in all versions of SSLeay and OpenSSL.
EVP_MD_CTX_init(),
EVP_MD_CTX_create(),
EVP_MD_CTX_copy_ex(),
EVP_MD_CTX_cleanup(),
EVP_MD_CTX_destroy(),
EVP_DigestInit_ex() and
EVP_DigestFinal_ex() were added in OpenSSL 0.9.7.
EVP_md_null(),
EVP_md2(),
EVP_md5(),
EVP_sha(),
EVP_sha1(),
EVP_dss(),
EVP_dss1(),
EVP_mdc2() and
EVP_ripemd160() were changed to return truely const EVP_MD * in OpenSSL
0.9.7.
The link between digests and signing algorithms was fixed in OpenSSL 1.0 and
later, so now
EVP_sha1() can be used with RSA and DSA; there is no need
to use
EVP_dss1() any more.
OpenSSL 1.0 and later does not include the MD2 digest algorithm in the default
configuration due to its security weaknesses.