The SHA_ and SHA1_ functions calculate a 160-bit cryptographic checksum (digest) for any number of input bytes. A cryptographic checksum is a one-way hash function; that is, it is computationally impractical to find the input corresponding to a particular output. This net result is a "fingerprint" of the input-data, which does not disclose the actual input.
SHA (or SHA-0) is the original Secure Hash Algorithm specified in FIPS 160. It was quickly proven insecure, and has been superseded by SHA-1. SHA-0 is included for compatibility purposes only.
The SHA1_Init, SHA1_Update, and SHA1_Final functions are the core functions. Allocate an
.Vt SHA_CTX , initialize it with SHA1_Init, run over the data with SHA1_Update, and finally extract the result using SHA1_Final.
SHA1_End is a wrapper for SHA1_Final which converts the return value to a 41-character (including the terminating \0) ASCII string which represents the 160 bits in hexadecimal.
SHA1_File calculates the digest of a file, and uses SHA1_End to return the result. If the file cannot be opened, a null pointer is returned. SHA1_FileChunk is similar to SHA1_File, but it only calculates the digest over a byte-range of the file specified, starting at offset and spanning length bytes. If the length parameter is specified as 0, or more than the length of the remaining part of the file, SHA1_FileChunk calculates the digest from offset to the end of file. SHA1_Data calculates the digest of a chunk of data in memory, and uses SHA1_End to return the result.
When using SHA1_End, SHA1_File, or SHA1_Data, the buf argument can be a null pointer, in which case the returned string is allocated with malloc(3) and subsequently must be explicitly deallocated using free(3) after use. If the buf argument is non-null it must point to at least 41 characters of buffer space.
md2(3), md4(3), md5(3), ripemd(3), sha256(3)