185 lines
4.6 KiB
Groff
185 lines
4.6 KiB
Groff
.\"
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.\" ----------------------------------------------------------------------------
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.\" "THE BEER-WARE LICENSE" (Revision 42):
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.\" <phk@FreeBSD.org> 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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.In sys/types.h
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.In 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.
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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.
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This net result is
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a
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.Dq fingerprint
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of the input-data, which does not disclose the actual 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.
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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.
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Allocate an
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.Vt SHA_CTX ,
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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 HISTORY
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These functions appeared in
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.Fx 4.0 .
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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 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 does not 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.
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Attempts 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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