A Chain Addition Generator in AWK

by Thumos

Justin Parrott's articles on keyspace iterators usking AWK (issue 38:3) and port scanners in Bash (issue 39:4) inspired me to try to stretch my scripting muscles.

Several months back, I'd fallen down the Wikipedia rabbit-hole and stumbled upon the VIC cipher.

I was intrigued by the cipher's use of chain addition as a sort of Lagged Fibonacci Generator and decided to see if I could write a chain addition generator in AWK.

The result is slow (almost seven minutes to create a 100 MB file) and not remotely close to cryptographically secure, but I considered it more an exercise in AWK than in cryptography.

An earlier version had the user input both the number of rounds and the key as command line options.  However, on a Linux system, this would leave the key in the user's shell history file, so I rewrote the script to ask for user input after it starts.

The script:

#!/bin/awk -f # chain-add: A chain addition generator # Thanks to Justin Parrott for the inspiration BEGIN { printf "Enter number of rounds: "; getline rounds < "/dev/stdin"; printf "Enter key: "; getline key < "/dev/stdin"; split(key, num, ""); len = length(num); for (i = 1; i <= rounds; i++) { num[len + i] = ((num[i] + num[i + 1]) % 10); printf num[len + i] }; print

Example:

$ ./chain.awk Enter number of rounds: 8192 Enter key: 1122334455 2345678907579135797226048266948642082532406280785646808753100488528410426370251468907276504797993154166682469572 2406054294646659613000214574300235921730258413803273254183590579591849526440923478084915715882306286360536804996 5894843851373227136400549849040593723944542095238996294751785813126853394438438623871271485158398523663127375929 4390024113729026524091928176490010983039011971332912068465103264201613580621774838683841211441125332585237865733 7505412060255953266270448582897482330076120563073732519370005760207005236227705759849475224723312746195643910704 1072017745179218419686139250544742175598116382047927910241619601265770561381247517419361268150297384965216012351 7376135868003748344803012178283313385001644613501708074851878871236955658359540113184494124492833536831016889414 1174673555281030800709133880779046168746940774510534741961587115057635826552398308107527138917279841708996725878 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Code: chain.awk