digest.h

All headers

Digest functions.

An EVP_MD abstracts the details of a specific hash function allowing code to deal with the concept of a "hash function" without needing to know exactly which hash function it is.

  1. Hash algorithms
  2. EVP_md4
  3. EVP_md5
  4. EVP_sha1
  5. EVP_sha224
  6. EVP_sha256
  7. EVP_sha384
  8. EVP_sha512
  9. EVP_md5_sha1
  10. EVP_get_digestbynid
  11. EVP_get_digestbyobj
  12. Digest contexts
  13. EVP_MD_CTX_init
  14. EVP_MD_CTX_create
  15. EVP_MD_CTX_cleanup
  16. EVP_MD_CTX_destroy
  17. EVP_MD_CTX_copy_ex
  18. Digest operations
  19. EVP_DigestInit_ex
  20. EVP_DigestInit
  21. EVP_DigestUpdate
  22. EVP_MAX_MD_SIZE
  23. EVP_MAX_MD_BLOCK_SIZE
  24. EVP_DigestFinal_ex
  25. EVP_DigestFinal
  26. EVP_Digest
  27. Digest function accessors
  28. EVP_MD_type
  29. EVP_MD_flags
  30. EVP_MD_size
  31. EVP_MD_block_size
  32. EVP_MD_FLAG_PKEY_DIGEST
  33. EVP_MD_FLAG_DIGALGID_ABSENT
  34. Deprecated functions
  35. EVP_MD_CTX_copy
  36. EVP_add_digest
  37. EVP_get_digestbyname
  38. EVP_dss1
  39. Digest operation accessors
  40. EVP_MD_CTX_md
  41. EVP_MD_CTX_size
  42. EVP_MD_CTX_block_size
  43. EVP_MD_CTX_type
  44. env_md_ctx_st

Hash algorithms.

The following functions return EVP_MD objects that implement the named hash function.

OPENSSL_EXPORT const EVP_MD *EVP_md4(void);
OPENSSL_EXPORT const EVP_MD *EVP_md5(void);
OPENSSL_EXPORT const EVP_MD *EVP_sha1(void);
OPENSSL_EXPORT const EVP_MD *EVP_sha224(void);
OPENSSL_EXPORT const EVP_MD *EVP_sha256(void);
OPENSSL_EXPORT const EVP_MD *EVP_sha384(void);
OPENSSL_EXPORT const EVP_MD *EVP_sha512(void);

EVP_md5_sha1 is a TLS-specific EVP_MD which computes the concatenation of MD5 and SHA-1, as used in TLS 1.1 and below.

OPENSSL_EXPORT const EVP_MD *EVP_md5_sha1(void);

EVP_get_digestbynid returns an EVP_MD for the given NID, or NULL if no such digest is known.

OPENSSL_EXPORT const EVP_MD *EVP_get_digestbynid(int nid);

EVP_get_digestbyobj returns an EVP_MD for the given ASN1_OBJECT, or NULL if no such digest is known.

OPENSSL_EXPORT const EVP_MD *EVP_get_digestbyobj(const ASN1_OBJECT *obj);

Digest contexts.

An EVP_MD_CTX represents the state of a specific digest operation in progress.

EVP_MD_CTX_init initialises an, already allocated, EVP_MD_CTX. This is the same as setting the structure to zero.

OPENSSL_EXPORT void EVP_MD_CTX_init(EVP_MD_CTX *ctx);

EVP_MD_CTX_create allocates and initialises a fresh EVP_MD_CTX and returns it, or NULL on allocation failure.

OPENSSL_EXPORT EVP_MD_CTX *EVP_MD_CTX_create(void);

EVP_MD_CTX_cleanup frees any resources owned by ctx and resets it to a freshly initialised state. It does not free ctx itself. It returns one.

OPENSSL_EXPORT int EVP_MD_CTX_cleanup(EVP_MD_CTX *ctx);

EVP_MD_CTX_destroy calls EVP_MD_CTX_cleanup and then frees ctx itself.

OPENSSL_EXPORT void EVP_MD_CTX_destroy(EVP_MD_CTX *ctx);

EVP_MD_CTX_copy_ex sets out, which must already be initialised, to be a copy of in. It returns one on success and zero on error.

OPENSSL_EXPORT int EVP_MD_CTX_copy_ex(EVP_MD_CTX *out, const EVP_MD_CTX *in);

Digest operations.

EVP_DigestInit_ex configures ctx, which must already have been initialised, for a fresh hashing operation using type. It returns one on success and zero otherwise.

OPENSSL_EXPORT int EVP_DigestInit_ex(EVP_MD_CTX *ctx, const EVP_MD *type,
                                     ENGINE *engine);

EVP_DigestInit acts like EVP_DigestInit_ex except that ctx is initialised before use.

OPENSSL_EXPORT int EVP_DigestInit(EVP_MD_CTX *ctx, const EVP_MD *type);

EVP_DigestUpdate hashes len bytes from data into the hashing operation in ctx. It returns one.

OPENSSL_EXPORT int EVP_DigestUpdate(EVP_MD_CTX *ctx, const void *data,
                                    size_t len);

EVP_MAX_MD_SIZE is the largest digest size supported, in bytes. Functions that output a digest generally require the buffer have at least this much space.

#define EVP_MAX_MD_SIZE 64  // SHA-512 is the longest so far.

EVP_MAX_MD_BLOCK_SIZE is the largest digest block size supported, in bytes.

#define EVP_MAX_MD_BLOCK_SIZE 128  // SHA-512 is the longest so far.

EVP_DigestFinal_ex finishes the digest in ctx and writes the output to md_out. EVP_MD_CTX_size bytes are written, which is at most EVP_MAX_MD_SIZE. If out_size is not NULL then *out_size is set to the number of bytes written. It returns one. After this call, the hash cannot be updated or finished again until EVP_DigestInit_ex is called to start another hashing operation.

OPENSSL_EXPORT int EVP_DigestFinal_ex(EVP_MD_CTX *ctx, uint8_t *md_out,
                                      unsigned int *out_size);

EVP_DigestFinal acts like EVP_DigestFinal_ex except that EVP_MD_CTX_cleanup is called on ctx before returning.

OPENSSL_EXPORT int EVP_DigestFinal(EVP_MD_CTX *ctx, uint8_t *md_out,
                                   unsigned int *out_size);

EVP_Digest performs a complete hashing operation in one call. It hashes len bytes from data and writes the digest to md_out. EVP_MD_CTX_size bytes are written, which is at most EVP_MAX_MD_SIZE. If out_size is not NULL then *out_size is set to the number of bytes written. It returns one on success and zero otherwise.

OPENSSL_EXPORT int EVP_Digest(const void *data, size_t len, uint8_t *md_out,
                              unsigned int *md_out_size, const EVP_MD *type,
                              ENGINE *impl);

Digest function accessors.

These functions allow code to learn details about an abstract hash function.

EVP_MD_type returns a NID identifying md. (For example, NID_sha256.)

OPENSSL_EXPORT int EVP_MD_type(const EVP_MD *md);

EVP_MD_flags returns the flags for md, which is a set of EVP_MD_FLAG_* values, ORed together.

OPENSSL_EXPORT uint32_t EVP_MD_flags(const EVP_MD *md);

EVP_MD_size returns the digest size of md, in bytes.

OPENSSL_EXPORT size_t EVP_MD_size(const EVP_MD *md);

EVP_MD_block_size returns the native block-size of md, in bytes.

OPENSSL_EXPORT size_t EVP_MD_block_size(const EVP_MD *md);

EVP_MD_FLAG_PKEY_DIGEST indicates the the digest function is used with a specific public key in order to verify signatures. (For example, EVP_dss1.)

#define EVP_MD_FLAG_PKEY_DIGEST 1

EVP_MD_FLAG_DIGALGID_ABSENT indicates that the parameter type in an X.509 DigestAlgorithmIdentifier representing this digest function should be undefined rather than NULL.

#define EVP_MD_FLAG_DIGALGID_ABSENT 2

Deprecated functions.

EVP_MD_CTX_copy sets out, which must /not/ be initialised, to be a copy of in. It returns one on success and zero on error.

OPENSSL_EXPORT int EVP_MD_CTX_copy(EVP_MD_CTX *out, const EVP_MD_CTX *in);

EVP_add_digest does nothing and returns one. It exists only for compatibility with OpenSSL.

OPENSSL_EXPORT int EVP_add_digest(const EVP_MD *digest);

EVP_get_digestbyname returns an EVP_MD given a human readable name in name, or NULL if the name is unknown.

OPENSSL_EXPORT const EVP_MD *EVP_get_digestbyname(const char *);

EVP_dss1 returns the value of EVP_sha1(). This was provided by OpenSSL to specifiy the original DSA signatures, which were fixed to use SHA-1. Note, however, that attempting to sign or verify DSA signatures with the EVP interface will always fail.

OPENSSL_EXPORT const EVP_MD *EVP_dss1(void);

Digest operation accessors.

EVP_MD_CTX_md returns the underlying digest function, or NULL if one has not been set.

OPENSSL_EXPORT const EVP_MD *EVP_MD_CTX_md(const EVP_MD_CTX *ctx);

EVP_MD_CTX_size returns the digest size of ctx, in bytes. It will crash if a digest hasn't been set on ctx.

OPENSSL_EXPORT size_t EVP_MD_CTX_size(const EVP_MD_CTX *ctx);

EVP_MD_CTX_block_size returns the block size of the digest function used by ctx, in bytes. It will crash if a digest hasn't been set on ctx.

OPENSSL_EXPORT size_t EVP_MD_CTX_block_size(const EVP_MD_CTX *ctx);

EVP_MD_CTX_type returns a NID describing the digest function used by ctx. (For example, NID_sha256.) It will crash if a digest hasn't been set on ctx.

OPENSSL_EXPORT int EVP_MD_CTX_type(const EVP_MD_CTX *ctx);
struct evp_md_pctx_ops;
struct env_md_ctx_st {
  // digest is the underlying digest function, or NULL if not set.
  const EVP_MD *digest;
  // md_data points to a block of memory that contains the hash-specific
  // context.
  void *md_data;

  // pctx is an opaque (at this layer) pointer to additional context that
  // EVP_PKEY functions may store in this object.
  EVP_PKEY_CTX *pctx;

  // pctx_ops, if not NULL, points to a vtable that contains functions to
  // manipulate |pctx|.
  const struct evp_md_pctx_ops *pctx_ops;
} /* EVP_MD_CTX */;