Class type Cryptokit.transform
class type transform = object end
A transform is an arbitrary mapping from sequences of characters
to sequences of characters. Examples of transforms include
ciphering, deciphering, compression, decompression, and encoding
of binary data as text. Input data to a transform is provided
by successive calls to the methods
put_substring, put_string,
put_char or put_byte. The result of transforming the input
data is buffered internally, and can be obtained via the
get_string, get_substring, get_char and get_byte methods.method put_substring : string -> int -> int -> unitput_substring str pos len processes len characters of
string str, starting at character number pos,
through the transform.method put_string : string -> unitput_string str processes all characters of string str
through the transform.method put_char : char -> unitput_char c processes character c through the transform.method put_byte : int -> unitput_byte b processes the character having code b
through the transform. b must be between 0 and 255
inclusive.method finish : unit
Call method
finish to indicate that no further data will
be processed through the transform. This causes the transform
to e.g. add final padding to the data and flush its internal
buffers. Raise Error Wrong_data_length if the total length
of input data provided via the put_* methods is not
an integral number of the input block size
(see Cryptokit.transform.input_block_size).
After calling finish, the transform can no longer accept
additional data. Hence, do not call any of the put_*
methods after calling finish.method available_output : int
Return the number of characters of output currently available.
The output can be recovered with the
get_* methods.method get_string : string
Return a character string containing all output characters
available at this point. The internal output buffer is emptied;
in other terms, all currently available output is consumed
(and returned to the caller) by a call to
get_string.method get_substring : string * int * int
Return a triple
(buf,pos,len), where buf is the internal
output buffer for the transform, pos the position of the
first character of available output, and len the number of
characters of available output. The string buf will be
modified later, so the caller must immediately copy
characters pos to pos+len-1 of buf to some other
location. The internal output buffer is emptied;
in other terms, all currently available output is consumed
(and returned to the caller) by a call to get_substring.method get_char : char
Return the first character of output, and remove it from the
internal output buffer. Raise
End_of_file if no output
is currently available.method get_byte : int
Return the code of the first character of output,
and remove it from the internal output buffer.
Raise
End_of_file if no output is currently available.method input_block_size : int
Some transforms (e.g. unpadded block ciphers) process
input data by blocks of several characters. This method
returns the size of input blocks for the current transform.
If
input_block_size > 1, the user of the transform
must ensure that the total length of input data provided
between the creation of the cipher and the call to
finish is an integral multiple of input_block_size.
If input_block_size = 1, the transform can accept
input data of arbitrary length.method output_block_size : int
Some transforms (e.g. block ciphers) always produce output
data by blocks of several characters. This method
returns the size of output blocks for the current transform.
If
input_block_size > 1, the total length of output data
produced by the transform is always an integral multiple
of output_block_size.
If output_block_size = 1, the transform produces output data
of arbitrary length.method wipe : unit
Erase all internal buffers and data structures of this transform,
overwriting them with zeroes. A transform may contain sensitive
data such as secret key-derived material, or parts of the
input or output data. Calling
wipe ensures that this sensitive
data will not remain in memory longer than strictly necessary,
thus making certain invasive attacks more difficult.
It is thus prudent practice to call wipe on every
transform that the program no longer needs.
After calling wipe, the transform is no longer in a working
state: do not call any other methods after calling wipe.