mirror of https://github.com/openssl/openssl.git
95 lines
3.2 KiB
Plaintext
95 lines
3.2 KiB
Plaintext
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The Message Digest subroutines.
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These routines require "evp.h" to be included.
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These functions are a higher level interface to the various message digest
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routines found in this library. As such, they allow the same code to be
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used to digest via different algorithms with only a change in an initial
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parameter. They are basically just a front-end to the MD2, MD5, SHA
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and SHA1
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routines.
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These routines all take a pointer to the following structure to specify
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which message digest algorithm to use.
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typedef struct evp_md_st
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{
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int type;
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int pkey_type;
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int md_size;
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void (*init)();
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void (*update)();
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void (*final)();
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int required_pkey_type; /*EVP_PKEY_xxx */
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int (*sign)();
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int (*verify)();
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} EVP_MD;
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If additional message digest algorithms are to be supported, a structure of
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this type needs to be declared and populated and then the Digest routines
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can be used with that algorithm. The type field is the object NID of the
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digest type (read the section on Objects for an explanation). The pkey_type
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is the Object type to use when the a message digest is generated by there
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routines and then is to be signed with the pkey algorithm. Md_size is
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the size of the message digest returned. Init, update
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and final are the relevant functions to perform the message digest function
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by parts. One reason for specifying the message digest to use via this
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mechanism is that if you only use md5, only the md5 routines will
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be included in you linked program. If you passed an integer
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that specified which message digest to use, the routine that mapped that
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integer to a set of message digest functions would cause all the message
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digests functions to be link into the code. This setup also allows new
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message digest functions to be added by the application.
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The six message digests defined in this library are
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EVP_MD *EVP_md2(void); /* RSA sign/verify */
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EVP_MD *EVP_md5(void); /* RSA sign/verify */
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EVP_MD *EVP_sha(void); /* RSA sign/verify */
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EVP_MD *EVP_sha1(void); /* RSA sign/verify */
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EVP_MD *EVP_dss(void); /* DSA sign/verify */
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EVP_MD *EVP_dss1(void); /* DSA sign/verify */
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All the message digest routines take a EVP_MD_CTX pointer as an argument.
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The state of the message digest is kept in this structure.
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typedef struct pem_md_ctx_st
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{
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EVP_MD *digest;
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union {
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unsigned char base[4]; /* this is used in my library as a
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* 'pointer' to all union elements
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* structures. */
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MD2_CTX md2;
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MD5_CTX md5;
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SHA_CTX sha;
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} md;
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} EVP_MD_CTX;
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The Digest functions are as follows.
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void EVP_DigestInit(
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EVP_MD_CTX *ctx,
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EVP_MD *type);
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This function is used to initialise the EVP_MD_CTX. The message
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digest that will associated with 'ctx' is specified by 'type'.
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void EVP_DigestUpdate(
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EVP_MD_CTX *ctx,
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unsigned char *data,
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unsigned int cnt);
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This function is used to pass more data to the message digest
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function. 'cnt' bytes are digested from 'data'.
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void EVP_DigestFinal(
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EVP_MD_CTX *ctx,
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unsigned char *md,
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unsigned int *len);
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This function finishes the digestion and puts the message digest
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into 'md'. The length of the message digest is put into len;
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EVP_MAX_MD_SIZE is the size of the largest message digest that
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can be returned from this function. Len can be NULL if the
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size of the digest is not required.
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