1780e40715
This implements SHA-512/256, which generates a 256 bit hash by calculating the SHA-512 then truncating the result. A different initial value is used, making the result different from the first 256 bits of the SHA-512 of the same input. SHA-512 is ~50% faster than SHA-256 on 64bit platforms, so the result is a faster 256 bit hash. The main goal of this implementation is to enable support for this faster hashing algorithm in ZFS. The feature was introduced into ZFS in r289422, but is disconnected because SHA-512/256 support was missing. A further commit will enable it in ZFS. This is the follow on to r292782 Reviewed by: cem Sponsored by: ScaleEngine Inc. Differential Revision: https://reviews.freebsd.org/D6061
208 lines
5.5 KiB
Groff
208 lines
5.5 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 April 22, 2016
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.Dt SHA512 3
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.Os
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.Sh NAME
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.Nm SHA512_Init ,
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.Nm SHA512_Update ,
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.Nm SHA512_Final ,
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.Nm SHA512_End ,
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.Nm SHA512_File ,
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.Nm SHA512_FileChunk ,
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.Nm SHA512_Data ,
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.Nm SHA384_Init ,
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.Nm SHA384_Update ,
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.Nm SHA384_Final ,
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.Nm SHA384_End ,
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.Nm SHA384_File ,
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.Nm SHA384_FileChunk ,
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.Nm SHA384_Data,
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.Nm SHA512_256_Init ,
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.Nm SHA512_256_Update ,
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.Nm SHA512_256_Final ,
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.Nm SHA512_256_End ,
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.Nm SHA512_256_File ,
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.Nm SHA512_256_FileChunk ,
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.Nm SHA512_256_Data
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.Nd calculate the FIPS 180-4 ``SHA-512'' family of 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 sha512.h
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.Ft void
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.Fn SHA512_Init "SHA512_CTX *context"
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.Ft void
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.Fn SHA512_Update "SHA512_CTX *context" "const unsigned char *data" "size_t len"
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.Ft void
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.Fn SHA512_Final "unsigned char digest[64]" "SHA512_CTX *context"
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.Ft "char *"
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.Fn SHA512_End "SHA512_CTX *context" "char *buf"
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.Ft "char *"
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.Fn SHA512_File "const char *filename" "char *buf"
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.Ft "char *"
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.Fn SHA512_FileChunk "const char *filename" "char *buf" "off_t offset" "off_t length"
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.Ft "char *"
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.Fn SHA512_Data "const unsigned char *data" "unsigned int len" "char *buf"
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.In sha384.h
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.Ft void
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.Fn SHA384_Init "SHA384_CTX *context"
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.Ft void
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.Fn SHA384_Update "SHA384_CTX *context" "const unsigned char *data" "size_t len"
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.Ft void
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.Fn SHA384_Final "unsigned char digest[48]" "SHA384_CTX *context"
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.Ft "char *"
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.Fn SHA384_End "SHA384_CTX *context" "char *buf"
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.Ft "char *"
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.Fn SHA384_File "const char *filename" "char *buf"
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.Ft "char *"
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.Fn SHA384_FileChunk "const char *filename" "char *buf" "off_t offset" "off_t length"
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.Ft "char *"
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.Fn SHA384_Data "const unsigned char *data" "unsigned int len" "char *buf"
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.In sha512t.h
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.Ft void
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.Fn SHA512_256_Init "SHA512_CTX *context"
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.Ft void
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.Fn SHA512_256_Update "SHA512_CTX *context" "const unsigned char *data" "size_t len"
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.Ft void
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.Fn SHA512_256_Final "unsigned char digest[32]" "SHA512_CTX *context"
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.Ft "char *"
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.Fn SHA512_256_End "SHA512_CTX *context" "char *buf"
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.Ft "char *"
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.Fn SHA512_256_File "const char *filename" "char *buf"
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.Ft "char *"
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.Fn SHA512_256_FileChunk "const char *filename" "char *buf" "off_t offset" "off_t length"
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.Ft "char *"
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.Fn SHA512_256_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 SHA512_
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functions calculate a 512-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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The
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.Fn SHA512_Init ,
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.Fn SHA512_Update ,
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and
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.Fn SHA512_Final
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functions are the core functions.
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Allocate an
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.Vt SHA512_CTX ,
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initialize it with
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.Fn SHA512_Init ,
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run over the data with
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.Fn SHA512_Update ,
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and finally extract the result using
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.Fn SHA512_Final .
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.Pp
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.Fn SHA512_End
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is a wrapper for
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.Fn SHA512_Final
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which converts the return value to a 129-character
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(including the terminating '\e0')
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.Tn ASCII
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string which represents the 512 bits in hexadecimal.
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.Pp
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.Fn SHA512_File
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calculates the digest of a file, and uses
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.Fn SHA512_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 SHA512_FileChunk
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is similar to
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.Fn SHA512_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 SHA512_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 SHA512_Data
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calculates the digest of a chunk of data in memory, and uses
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.Fn SHA512_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 SHA512_End ,
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.Fn SHA512_File ,
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or
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.Fn SHA512_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 129 characters of buffer space.
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.Pp
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The
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.Li SHA384_
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and
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.Li SHA512_256_
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functions are identical to the
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.Li SHA512_
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functions except they use a different initial hash value and the output is
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truncated to 384 bits and 256 bits respectively.
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.Pp
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.Fn SHA384_End
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is a wrapper for
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.Fn SHA384_Final
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which converts the return value to a 97-character
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(including the terminating '\e0')
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.Tn ASCII
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string which represents the 384 bits in hexadecimal.
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.Pp
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.Fn SHA512_256_End
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is a wrapper for
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.Fn SHA512_Final
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which converts the return value to a 65-character
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(including the terminating '\e0')
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.Tn ASCII
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string which represents the 256 bits in hexadecimal.
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.Sh SEE ALSO
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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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.Xr sha 3
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.Sh HISTORY
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These functions appeared in
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.Fx 9.0 .
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.Sh AUTHORS
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The core hash routines were implemented by Colin Percival based on
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the published
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.Tn FIPS 180-2
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standard.
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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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