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.Dd May 28, 2016
.Dt SKEIN 3
.Os
.Sh NAME
.Nm SKEIN256_Init ,
.Nm SKEIN256_Update ,
.Nm SKEIN256_Final ,
.Nm SKEIN256_End ,
.Nm SKEIN256_File ,
.Nm SKEIN256_FileChunk ,
.Nm SKEIN256_Data ,
.Nm SKEIN512_Init ,
.Nm SKEIN512_Update ,
.Nm SKEIN512_Final ,
.Nm SKEIN512_End ,
.Nm SKEIN512_File ,
.Nm SKEIN512_FileChunk ,
.Nm SKEIN512_Data ,
.Nm SKEIN1024_Init ,
.Nm SKEIN1024_Update ,
.Nm SKEIN1024_Final ,
.Nm SKEIN1024_End ,
.Nm SKEIN1024_File ,
.Nm SKEIN1024_FileChunk ,
.Nm SKEIN1024_Data
.Nd calculate the ``SKEIN'' family of message digests
.Sh LIBRARY
.Lb libmd
.Sh SYNOPSIS
.In sys/types.h
.In skein.h
.Ft void
.Fn SKEIN256_Init "SKEIN256_CTX *context"
.Ft void
.Fn SKEIN256_Update "SKEIN256_CTX *context" "const unsigned char *data" "size_t len"
.Ft void
.Fn SKEIN256_Final "unsigned char digest[32]" "SKEIN256_CTX *context"
.Ft "char *"
.Fn SKEIN256_End "SKEIN256_CTX *context" "char *buf"
.Ft "char *"
.Fn SKEIN256_File "const char *filename" "char *buf"
.Ft "char *"
.Fn SKEIN256_FileChunk "const char *filename" "char *buf" "off_t offset" "off_t length"
.Ft "char *"
.Fn SKEIN256_Data "const unsigned char *data" "unsigned int len" "char *buf"
.Ft void
.Fn SKEIN512_Init "SKEIN512_CTX *context"
.Ft void
.Fn SKEIN512_Update "SKEIN512_CTX *context" "const unsigned char *data" "size_t len"
.Ft void
.Fn SKEIN512_Final "unsigned char digest[64]" "SKEIN512_CTX *context"
.Ft "char *"
.Fn SKEIN512_End "SKEIN512_CTX *context" "char *buf"
.Ft "char *"
.Fn SKEIN512_File "const char *filename" "char *buf"
.Ft "char *"
.Fn SKEIN512_FileChunk "const char *filename" "char *buf" "off_t offset" "off_t length"
.Ft "char *"
.Fn SKEIN512_Data "const unsigned char *data" "unsigned int len" "char *buf"
.Ft void
.Fn SKEIN1024_Init "SKEIN1024_CTX *context"
.Ft void
.Fn SKEIN1024_Update "SKEIN1024_CTX *context" "const unsigned char *data" "size_t len"
.Ft void
.Fn SKEIN1024_Final "unsigned char digest[128]" "SKEIN1024_CTX *context"
.Ft "char *"
.Fn SKEIN1024_End "SKEIN1024_CTX *context" "char *buf"
.Ft "char *"
.Fn SKEIN1024_File "const char *filename" "char *buf"
.Ft "char *"
.Fn SKEIN1024_FileChunk "const char *filename" "char *buf" "off_t offset" "off_t length"
.Ft "char *"
.Fn SKEIN1024_Data "const unsigned char *data" "unsigned int len" "char *buf"
.Sh DESCRIPTION
.Li Skein
is a new family of cryptographic hash functions based on the
.Li Threefish
large-block cipher.
Its design combines speed, security, simplicity, and a great deal of
flexibility in a modular package that is easy to analyze.
.Li Skein
is defined for three different internal state sizes\(em256 bits, 512 bits, and
1024 bits\(emand any output size.
This allows Skein to be a drop-in replacement for the entire SHA family
of hash functions.
.Pp
The
.Fn SKEIN256_Init ,
.Fn SKEIN256_Update ,
and
.Fn SKEIN256_Final
functions are the core functions.
Allocate an
.Vt SKEIN256_CTX ,
initialize it with
.Fn SKEIN256_Init ,
run over the data with
.Fn SKEIN256_Update ,
and finally extract the result using
.Fn SKEIN256_Final ,
which will also erase the
.Vt SKEIN256_CTX .
.Pp
.Fn SKEIN256_End
is a wrapper for
.Fn SKEIN256_Final
which converts the return value to a 33-character
(including the terminating '\e0')
.Tn ASCII
string which represents the 256 bits in hexadecimal.
.Pp
.Fn SKEIN256_File
calculates the digest of a file, and uses
.Fn SKEIN256_End
to return the result.
If the file cannot be opened, a null pointer is returned.
.Fn SKEIN256_FileChunk
is similar to
.Fn SKEIN256_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 SKEIN256_FileChunk
calculates the digest from
.Fa offset
to the end of file.
.Fn SKEIN256_Data
calculates the digest of a chunk of data in memory, and uses
.Fn SKEIN256_End
to return the result.
.Pp
When using
.Fn SKEIN256_End ,
.Fn SKEIN256_File ,
or
.Fn SKEIN256_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 33 characters of buffer space.
.Pp
The
.Li SKEIN512_
and
.Li SKEIN1024_
functions are similar to the
.Li SKEIN256_
functions except they produce a 512-bit, 65 character,
or 1024-bit, 129 character, output.
.Sh SEE ALSO
.Xr md4 3 ,
.Xr md5 3 ,
.Xr ripemd 3 ,
.Xr sha 3 ,
.Xr sha256 3 ,
.Xr sha512 3
.Sh HISTORY
These functions appeared in
.Fx 11.0 .
.Sh AUTHORS
.An -nosplit
The core hash routines were imported from version 1.3 of the optimized 
Skein reference implementation written by
.An Doug Whiting
as submitted to the NSA SHA-3 contest.
The algorithms were developed by
.An Niels Ferguson , 
.An Stefan Lucks ,
.An Bruce Schneier , 
.An Doug Whiting , 
.An Mihir Bellare ,
.An Tadayoshi Kohno ,
.An Jon Callas,
and
.An Jesse Walker .