NAME

SYNOPSIS

DESCRIPTION

cipherProc configure ?options?

Configure the settings for the gronsfeld cipher. Valid options are:

cipherProc configure -ciphertext string

cipherProc configure -ct string

Set the ciphertext for this cipher instance to string. Invalid letters or numbers in the ciphertext are silently discarded.

cipherProc configure -period n

Set the period for this cipher to n.

cipherProc configure -stepinterval n

Set the display interval while solving to n. The stepcommand procedure will be called for every nth iteration while solving. This is used to provide user feedback while solving is taking place.

cipherProc configure -stepcommand proc

Set the display command while solving to proc. This command will be called for every nth iteration while solving. The arguments for this procedure are:

stepcommand iter key pt

iter is the current iteration number. key is the current value of the key that is being used. pt is the plaintext that is produced with this key.

cipherProc configure -bestfitcommand proc

Set the best fit display command while solving to proc. This command will be called every time a better solution is found while autosolving. The arguments for this procedure are:

bestfitcommand iter key value pt

iter is the current iteration number. key is the current value of the key that is being used. value is the value of the metric used to judge how good this solution is. The value is often a digram or trigram frequency count. pt is the plaintext that is produced with this key.

cipherProc configure -language language

This option is currently ignored for all cipher types. Set the current cipher language to language. If the cipher has a solve method then digram frequencies for this language are used to determine the best fit. If the language is not specified or not known then english is used.

cipherProc configure -solvemethod fast|thorough

gronsfeld ciphers have two possible autosolve methods. The first method, fast, finds the best digram fit for the first and second columns. It then fixes the key for the first two columns and then finds the best digram fit for the second and third column. The third column's key is then fixed. This procedure is repeated for all of the columns in the cipher. This method is very quick, but has the drawback that if an error is made in the key for one of the first few columns, the error may propogate through and the resulting solution could be far from correct.

The second method, thorough, performs a brute force search through every possible key. This takes much longer since it must search the keyspace for 26^period possible keys.

A digram frequency count is used to determine which key is the most likely.

cipherProc cget option

Look up the value for a given option. Valid options are:

cipherProc cget -type

Returns the type of this cipher. In this case, gronsfeld

cipherProc cget -ciphertext

cipherProc cget -ct

Return the ciphertext for this cipher.

cipherProc cget -plaintext

cipherProc cget -pt

Return the plaintext for this cipher based on the current key setting.

cipherProc cget -key

Returns the current key setting for this cipher. The result can be passed back to this cipher instance or another cipher with the cipherProc restore subcommand.

cipherProc cget -keyword

Returns the keyword for this cipher based on the current key.

cipherProc cget -length

Returns the length of the ciphertext for this cipher. 0 is returned if the ciphertext has not been set.

cipherProc cget -period

Return the period for this cipher.

cipherProc cget -stepinterval

Returns the current value of the stepinterval.

cipherProc cget -stepcommand

Returns the name of the procedure currently set for the stepcommand. An empty string is returned if no stepcommand is set.

cipherProc cget -bestfitcommand

Returns the name of the procedure currently set for the bestfitcommand. An empty string is returned if no bestfitcommand is set.

cipherProc cget -language

Returns the name of the language used for this cipher.

cipherProc cget -solvemethod

Returns the current setting for the solvemethod option, either fast or thorough.

cipherProc substitute ct pt column

Substitutes the ct string for pt starting at column. pt does not need to appear in the ciphertext. ct and pt must be the same length. The substitute command calculates what key letter(s) would produce the specified ct from the pt and enters it in the cipher's key. After performing a substitution, you can use the cipherProc cget -plaintext command to look at the rest of the substitutions that the key change produced.

cipherProc undo column

The undo command erases the key entry for the specified column.

cipherProc restore ct pt

The restore command restores the cipher's key to a previously stored state. The output from cipherProc cget -key can be passed back into the restore command to implement a crude save feature. Example:

set key [$firstCipher cget -key]
$secondCipher restore [lindex $key 0] [lindex $key 1]

It operates the same as if you had run cipherProc substitute ct pt 0.

cipherProc locate tip ?ct?

Locate a possible position for the tip in the ciphertext. The tip is dragged along the ciphertext until a valid substitution is found. If the ct argument is specified, the tip is dragged along starting where ct appears in the ciphertext.

cipherProc locatebest tip

This routine drags the tip through all of the positions in the ciphertext and returns the one that produces the best plaintext, as determined by digram frequencies.

cipherProc fit column

This routines tries all 26 possible keys for the given column and returns the one that produces the best single-letter frequency count.

cipherProc solve

Solve the current cipher. Solutions are found by looping through a set of keys and calculating the frequency of the digrams in the resulting plaintext. The key that produces the highest digram frequency count will be listed as being the most likely solution. In order to provide some user feedback (to let you know that it's actually running), the solve method can be set to call a user-defined procedure at every nth key that is tried. See the descriptions for -stepcommand and -stepinterval on how to use this feature. The solve routine will also call a user-defined procedure every time it finds a solution better than the currentbest. The -bestfitcommand option describes this in more detail.
When this command returns, it will set the current key for the cipher to the best one that was found.