2 .\" ----------------------------------------------------------------------------
3 .\" "THE BEER-WARE LICENSE" (Revision 42):
4 .\" <phk@login.dkuug.dk> wrote this file. As long as you retain this notice you
5 .\" can do whatever you want with this stuff. If we meet some day, and you think
6 .\" this stuff is worth it, you can buy me a beer in return. Poul-Henning Kamp
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9 .\" From: Id: mdX.3,v 1.14 1999/02/11 20:31:49 wollman Exp
10 .\" $FreeBSD: src/lib/libmd/sha.3,v 1.4.2.5 2001/12/17 10:08:31 ru Exp $
28 .Nd calculate the FIPS 160 and 160-1 ``SHA'' message digests
35 .Fn SHA_Init "SHA_CTX *context"
37 .Fn SHA_Update "SHA_CTX *context" "const unsigned char *data" "unsigned int len"
39 .Fn SHA_Final "unsigned char digest[20]" "SHA_CTX *context"
41 .Fn SHA_End "SHA_CTX *context" "char *buf"
43 .Fn SHA_File "const char *filename" "char *buf"
45 .Fn SHA_Data "const unsigned char *data" "unsigned int len" "char *buf"
47 .Fn SHA1_Init "SHA_CTX *context"
49 .Fn SHA1_Update "SHA_CTX *context" "const unsigned char *data" "unsigned int len"
51 .Fn SHA1_Final "unsigned char digest[20]" "SHA_CTX *context"
53 .Fn SHA1_End "SHA_CTX *context" "char *buf"
55 .Fn SHA1_File "const char *filename" "char *buf"
57 .Fn SHA1_Data "const unsigned char *data" "unsigned int len" "char *buf"
63 functions calculate a 160-bit cryptographic checksum (digest)
64 for any number of input bytes. A cryptographic checksum is a one-way
65 hash function; that is, it is computationally impractical to find
66 the input corresponding to a particular output. This net result is
67 a ``fingerprint'' of the input-data, which doesn't disclose the actual
73 is the original Secure Hash Algorithm specified in
75 160. It was quickly proven insecure, and has been superseded by
78 is included for compatibility purposes only.
85 functions are the core functions. Allocate an SHA_CTX, initialize it with
87 run over the data with
89 and finally extract the result using
95 which converts the return value to a 41-character
96 (including the terminating '\e0')
98 string which represents the 160 bits in hexadecimal.
101 calculates the digest of a file, and uses
103 to return the result.
104 If the file cannot be opened, a null pointer is returned.
106 calculates the digest of a chunk of data in memory, and uses
108 to return the result.
117 argument can be a null pointer, in which case the returned string
120 and subsequently must be explicitly deallocated using
125 argument is non-null it must point to at least 41 characters of buffer space.
132 The core hash routines were implemented by Eric Young based on the
137 These functions appeared in
140 No method is known to exist which finds two files having the same hash value,
141 nor to find a file with a specific hash value.
142 There is on the other hand no guarantee that such a method doesn't exist.
146 (Intel) implementation of
148 makes heavy use of the
150 instruction, which is not present on the original 80386. Attempts
153 on those processors will cause an illegal instruction trap.
154 (Arguably, the kernel should simply emulate this instruction.)