freebsd-skq/lib/libmd/ripemd.3

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.Dd July 20, 2018
.Dt RIPEMD 3
.Os
.Sh NAME
.Nm RIPEMD160_Init ,
.Nm RIPEMD160_Update ,
.Nm RIPEMD160_Final ,
.Nm RIPEMD160_End ,
.Nm RIPEMD160_File ,
.Nm RIPEMD160_FileChunk ,
.Nm RIPEMD160_Data
.Nd calculate the RIPEMD160 message digest
.Sh LIBRARY
.Lb libmd
.Sh SYNOPSIS
.In sys/types.h
.In ripemd.h
.Ft void
.Fn RIPEMD160_Init "RIPEMD160_CTX *context"
.Ft void
.Fn RIPEMD160_Update "RIPEMD160_CTX *context" "const unsigned char *data" "unsigned int len"
.Ft void
.Fn RIPEMD160_Final "unsigned char digest[20]" "RIPEMD160_CTX *context"
.Ft "char *"
.Fn RIPEMD160_End "RIPEMD160_CTX *context" "char *buf"
.Ft "char *"
.Fn RIPEMD160_File "const char *filename" "char *buf"
.Ft "char *"
.Fn RIPEMD160_FileChunk "const char *filename" "char *buf" "off_t offset" "off_t length"
.Ft "char *"
.Fn RIPEMD160_Data "const unsigned char *data" "unsigned int len" "char *buf"
.Sh DESCRIPTION
The
.Li RIPEMD160_
functions calculate a 160-bit cryptographic checksum (digest)
for any number of input bytes.
A cryptographic checksum is a one-way
hash function; that is, it is computationally impractical to find
the input corresponding to a particular output.
This net result is a
.Dq fingerprint
of the input-data, which does not disclose the actual input.
.Pp
The
.Fn RIPEMD160_Init ,
.Fn RIPEMD160_Update ,
and
.Fn RIPEMD160_Final
functions are the core functions.
Allocate an
.Vt RIPEMD160_CTX ,
initialize it with
.Fn RIPEMD160_Init ,
run over the data with
.Fn RIPEMD160_Update ,
and finally extract the result using
.Fn RIPEMD160_Final ,
which will also erase the
.Vt RIPEMD160_CTX .
.Pp
The
.Fn RIPEMD160_End
function is a wrapper for
.Fn RIPEMD160_Final
which converts the return value to a 41-character
(including the terminating '\e0')
.Tn ASCII
string which represents the 160 bits in hexadecimal.
.Pp
The
.Fn RIPEMD160_File
function calculates the digest of a file, and uses
.Fn RIPEMD160_End
to return the result.
If the file cannot be opened, a null pointer is returned.
The
.Fn RIPEMD160_FileChunk
function is similar to
.Fn RIPEMD160_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 RIPEMD160_FileChunk
calculates the digest from
.Fa offset
to the end of file.
The
.Fn RIPEMD160_Data
function calculates the digest of a chunk of data in memory, and uses
.Fn RIPEMD160_End
to return the result.
.Pp
When using
.Fn RIPEMD160_End ,
.Fn RIPEMD160_File ,
or
.Fn RIPEMD160_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 41 characters of buffer space.
.Sh ERRORS
The
.Fn RIPEMD160_End
function called with a null buf argument may fail and return NULL if:
.Bl -tag -width Er
.It Bq Er ENOMEM
Insufficient storage space is available.
.El
.Pp
The
.Fn RIPEMD160_File
and
.Fn RIPEMD160_FileChunk
may return NULL when underlying
.Xr open 2 ,
.Xr fstat 2 ,
.Xr lseek 2 ,
or
.Xr RIPEMD160_End 2
fail.
.Sh SEE ALSO
.Xr md4 3 ,
.Xr md5 3 ,
.Xr sha 3 ,
.Xr sha256 3 ,
.Xr sha512 3 ,
.Xr skein 3
.Sh HISTORY
These functions appeared in
.Fx 4.0 .
.Sh AUTHORS
The core hash routines were implemented by Eric Young based on the
published
.Tn RIPEMD160
specification.
.Sh BUGS
No method is known to exist which finds two files having the same hash value,
nor to find a file with a specific hash value.
There is on the other hand no guarantee that such a method does not exist.