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"THE BEER-WARE LICENSE" (Revision 42):
<phk@FreeBSD.org> wrote this file. As long as you retain this notice you
can do whatever you want with this stuff. If we meet some day, and you think
this stuff is worth it, you can buy me a beer in return. Poul-Henning Kamp
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From: Id: mdX.3,v 1.14 1999/02/11 20:31:49 wollman Exp
$FreeBSD: releng/10.3/lib/libmd/sha.3 263955 2014-03-31 00:28:54Z gjb $
.Dd March 28, 2014 .Dt SHA 3 .Os .Sh NAME .Nm SHA_Init , .Nm SHA_Update , .Nm SHA_Final , .Nm SHA_End , .Nm SHA_File , .Nm SHA_FileChunk , .Nm SHA_Data , .Nm SHA1_Init , .Nm SHA1_Update , .Nm SHA1_Final , .Nm SHA1_End , .Nm SHA1_File , .Nm SHA1_FileChunk , .Nm SHA1_Data .Nd calculate the FIPS 160 and 160-1 ``SHA'' message digests .Sh LIBRARY .Lb libmd .Sh SYNOPSIS n sys/types.h n sha.h .Ft void .Fn SHA_Init "SHA_CTX *context" .Ft void .Fn SHA_Update "SHA_CTX *context" "const unsigned char *data" "size_t len" .Ft void .Fn SHA_Final "unsigned char digest[20]" "SHA_CTX *context" .Ft "char *" .Fn SHA_End "SHA_CTX *context" "char *buf" .Ft "char *" .Fn SHA_File "const char *filename" "char *buf" .Ft "char *" .Fn SHA_FileChunk "const char *filename" "char *buf" "off_t offset" "off_t length" .Ft "char *" .Fn SHA_Data "const unsigned char *data" "unsigned int len" "char *buf" .Ft void .Fn SHA1_Init "SHA_CTX *context" .Ft void .Fn SHA1_Update "SHA_CTX *context" "const unsigned char *data" "size_t len" .Ft void .Fn SHA1_Final "unsigned char digest[20]" "SHA_CTX *context" .Ft "char *" .Fn SHA1_End "SHA_CTX *context" "char *buf" .Ft "char *" .Fn SHA1_File "const char *filename" "char *buf" .Ft "char *" .Fn SHA1_FileChunk "const char *filename" "char *buf" "off_t offset" "off_t length" .Ft "char *" .Fn SHA1_Data "const unsigned char *data" "unsigned int len" "char *buf" .Sh DESCRIPTION The .Li SHA_ and .Li 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 .Dq fingerprint of the input-data, which does not disclose the actual input.
p .Tn SHA (or .Tn SHA-0 ) is the original Secure Hash Algorithm specified in .Tn FIPS 160. It was quickly proven insecure, and has been superseded by .Tn SHA-1 . .Tn SHA-0 is included for compatibility purposes only.
p The .Fn SHA1_Init , .Fn SHA1_Update , and .Fn SHA1_Final functions are the core functions. Allocate an .Vt SHA_CTX , initialize it with .Fn SHA1_Init , run over the data with .Fn SHA1_Update , and finally extract the result using .Fn SHA1_Final .
p .Fn SHA1_End is a wrapper for .Fn SHA1_Final which converts the return value to a 41-character (including the terminating '\e0') .Tn ASCII string which represents the 160 bits in hexadecimal.
p .Fn SHA1_File calculates the digest of a file, and uses .Fn SHA1_End to return the result. If the file cannot be opened, a null pointer is returned. .Fn SHA1_FileChunk is similar to .Fn SHA1_File , but it only calculates the digest over a byte-range of the file specified, starting at .Fa offset and spanning .Fa length bytes. If the .Fa length parameter is specified as 0, or more than the length of the remaining part of the file, .Fn SHA1_FileChunk calculates the digest from .Fa offset to the end of file. .Fn SHA1_Data calculates the digest of a chunk of data in memory, and uses .Fn SHA1_End to return the result.
p When using .Fn SHA1_End , .Fn SHA1_File , or .Fn SHA1_Data , the .Fa buf argument can be a null pointer, in which case the returned string is allocated with .Xr malloc 3 and subsequently must be explicitly deallocated using .Xr free 3 after use. If the .Fa buf argument is non-null it must point to at least 41 characters of buffer space. .Sh SEE ALSO .Xr md4 3 , .Xr md5 3 , .Xr ripemd 3 , .Xr sha256 3 .Sh HISTORY These functions appeared in .Fx 4.0 . .Sh AUTHORS The core hash routines were implemented by Eric Young based on the published .Tn FIPS standards. .Sh BUGS No method is known to exist which finds two files having the same hash value, nor to find a file with a specific hash value. There is on the other hand no guarantee that such a method does not exist.
p The .Tn IA32 (Intel) implementation of .Tn SHA-1 makes heavy use of the .Ql bswapl instruction, which is not present on the original 80386. Attempts to use .Tn SHA-1 on those processors will cause an illegal instruction trap. (Arguably, the kernel should simply emulate this instruction.)