The SHA1 functions implement the NIST Secure Hash Algorithm (SHA-1), FIPS PUB 180-1. SHA-1 is used to generate a condensed representation of a message called a message digest. The algorithm takes a message less than 2^64 bits as input and produces a 160-bit digest suitable for use as a digital signature.
The SHA1 functions are considered to be more secure than the
md4(3) and
md5(3) functions with which they share a similar interface.
The
SHA1Init() function initializes a SHA1_CTX
context for use with
SHA1Update(), and
SHA1Final(). The
SHA1Update() function adds
data of length
len to the SHA1_CTX specified by
context.
SHA1Final() is called when all data has been added via
SHA1Update() and stores a message digest in the
digest parameter. When a null pointer is passed to
SHA1Final() as first argument only the final padding will be applied and the current context can still be used with
SHA1Update().
The
SHA1Transform() function is used by
SHA1Update() to hash 512-bit blocks and forms the core of the algorithm. Most programs should use the interface provided by
SHA1Init(),
SHA1Update() and
SHA1Final() instead of calling
SHA1Transform() directly.
The
SHA1End() function is a front end for
SHA1Final() which converts the digest into an ASCII representation of the 160 bit digest in hexadecimal.
The
SHA1File() function calculates the digest for a file and returns the result via
SHA1End(). If
SHA1File() is unable to open the file a NULL pointer is returned.
The
SHA1Data() function calculates the digest of an arbitrary string and returns the result via
SHA1End().
For each of the
SHA1End(),
SHA1File(), and
SHA1Data() functions the
buf parameter should either be a string of at least 41 characters in size or a NULL pointer. In the latter case, space will be dynamically allocated via
malloc(3) and should be freed using
free(3) when it is no longer needed.