c4d9468ea0
Avoid using parenthesis enclosure macros (.Pq and .Po/.Pc) with plain text. Not only this slows down the mdoc(7) processing significantly, but it also has an undesired (in this case) effect of disabling hyphenation within the entire enclosed block.
178 lines
4.6 KiB
Groff
178 lines
4.6 KiB
Groff
.\"
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.\" ----------------------------------------------------------------------------
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.\" "THE BEER-WARE LICENSE" (Revision 42):
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.\" <phk@login.dkuug.dk> wrote this file. As long as you retain this notice you
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.\" can do whatever you want with this stuff. If we meet some day, and you think
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.\" this stuff is worth it, you can buy me a beer in return. Poul-Henning Kamp
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.\" ----------------------------------------------------------------------------
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.\"
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.\" From: Id: mdX.3,v 1.14 1999/02/11 20:31:49 wollman Exp
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.\" $FreeBSD$
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.\"
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.Dd February 25, 1999
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.Dt SHA 3
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.Os
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.Sh NAME
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.Nm SHA_Init ,
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.Nm SHA_Update ,
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.Nm SHA_Final ,
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.Nm SHA_End ,
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.Nm SHA_File ,
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.Nm SHA_FileChunk ,
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.Nm SHA_Data ,
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.Nm SHA1_Init ,
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.Nm SHA1_Update ,
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.Nm SHA1_Final ,
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.Nm SHA1_End ,
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.Nm SHA1_File ,
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.Nm SHA1_FileChunk ,
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.Nm SHA1_Data
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.Nd calculate the FIPS 160 and 160-1 ``SHA'' message digests
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.Sh LIBRARY
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.Lb libmd
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.Sh SYNOPSIS
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.Fd #include <sys/types.h>
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.Fd #include <sha.h>
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.Ft void
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.Fn SHA_Init "SHA_CTX *context"
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.Ft void
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.Fn SHA_Update "SHA_CTX *context" "const unsigned char *data" "unsigned int len"
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.Ft void
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.Fn SHA_Final "unsigned char digest[20]" "SHA_CTX *context"
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.Ft "char *"
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.Fn SHA_End "SHA_CTX *context" "char *buf"
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.Ft "char *"
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.Fn SHA_File "const char *filename" "char *buf"
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.Ft "char *"
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.Fn SHA_FileChunk "const char *filename" "char *buf" "off_t offset" "off_t length"
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.Ft "char *"
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.Fn SHA_Data "const unsigned char *data" "unsigned int len" "char *buf"
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.Ft void
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.Fn SHA1_Init "SHA_CTX *context"
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.Ft void
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.Fn SHA1_Update "SHA_CTX *context" "const unsigned char *data" "unsigned int len"
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.Ft void
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.Fn SHA1_Final "unsigned char digest[20]" "SHA_CTX *context"
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.Ft "char *"
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.Fn SHA1_End "SHA_CTX *context" "char *buf"
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.Ft "char *"
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.Fn SHA1_File "const char *filename" "char *buf"
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.Ft "char *"
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.Fn SHA1_FileChunk "const char *filename" "char *buf" "off_t offset" "off_t length"
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.Ft "char *"
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.Fn SHA1_Data "const unsigned char *data" "unsigned int len" "char *buf"
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.Sh DESCRIPTION
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The
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.Li SHA_
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and
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.Li SHA1_
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functions calculate a 160-bit cryptographic checksum (digest)
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for any number of input bytes. A cryptographic checksum is a one-way
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hash function; that is, it is computationally impractical to find
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the input corresponding to a particular output. This net result is
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a ``fingerprint'' of the input-data, which doesn't disclose the actual
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input.
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.Pp
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.Tn SHA
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(or
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.Tn SHA-0 )
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is the original Secure Hash Algorithm specified in
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.Tn FIPS
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160. It was quickly proven insecure, and has been superseded by
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.Tn SHA-1 .
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.Tn SHA-0
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is included for compatibility purposes only.
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.Pp
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The
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.Fn SHA1_Init ,
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.Fn SHA1_Update ,
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and
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.Fn SHA1_Final
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functions are the core functions. Allocate an SHA_CTX, initialize it with
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.Fn SHA1_Init ,
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run over the data with
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.Fn SHA1_Update ,
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and finally extract the result using
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.Fn SHA1_Final .
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.Pp
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.Fn SHA1_End
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is a wrapper for
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.Fn SHA1_Final
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which converts the return value to a 41-character
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(including the terminating '\e0')
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.Tn ASCII
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string which represents the 160 bits in hexadecimal.
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.Pp
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.Fn SHA1_File
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calculates the digest of a file, and uses
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.Fn SHA1_End
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to return the result.
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If the file cannot be opened, a null pointer is returned.
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.Fn SHA1_FileChunk
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is similar to
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.Fn SHA1_File ,
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but it only calculates the digest over a byte-range of the file specified,
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starting at
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.Fa offset
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and spanning
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.Fa length
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bytes.
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If the
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.Fa length
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parameter is specified as 0, or more than the length of the remaining part
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of the file,
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.Fn SHA1_FileChunk
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calculates the digest from
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.Fa offset
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to the end of file.
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.Fn SHA1_Data
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calculates the digest of a chunk of data in memory, and uses
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.Fn SHA1_End
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to return the result.
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.Pp
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When using
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.Fn SHA1_End ,
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.Fn SHA1_File ,
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or
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.Fn SHA1_Data ,
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the
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.Fa buf
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argument can be a null pointer, in which case the returned string
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is allocated with
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.Xr malloc 3
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and subsequently must be explicitly deallocated using
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.Xr free 3
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after use.
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If the
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.Fa buf
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argument is non-null it must point to at least 41 characters of buffer space.
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.Sh SEE ALSO
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.Xr md2 3 ,
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.Xr md4 3 ,
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.Xr md5 3 ,
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.Xr ripemd 3
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.Sh AUTHORS
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The core hash routines were implemented by Eric Young based on the
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published
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.Tn FIPS
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standards.
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.Sh HISTORY
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These functions appeared in
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.Fx 4.0 .
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.Sh BUGS
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No method is known to exist which finds two files having the same hash value,
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nor to find a file with a specific hash value.
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There is on the other hand no guarantee that such a method doesn't exist.
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.Pp
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The
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.Tn IA32
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(Intel) implementation of
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.Tn SHA-1
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makes heavy use of the
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.Ql bswapl
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instruction, which is not present on the original 80386. Attempts
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to use
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.Tn SHA-1
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on those processors will cause an illegal instruction trap.
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(Arguably, the kernel should simply emulate this instruction.)
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