Computer Security and Cryptography

2.11 COLUMNAR TRANSPOSITION PROBLEMS

Problems 2.1–2.6 provide examples to which cribbing should be applied. The subject matter and a range of possible widths N is provided in each problem. A complete solution requires

1. Use of the subject matter to guess a set of possible cribs;
2. A program to search ciphertext for cribs;
3. Determination of the set of possible widths N consistent with the occurrence of the crib;
4. Recovery of the transposition τ = (τ₀, τ₁, …, τ_n−1); and
5. Decipherment of the ciphertext.

The ciphertext files cipherPr2.1–cipherPr2.12 may be downloaded from the following ftp address: ftp://ftp.wiley.com/public/sci_tech_med/computer_security.

PROBLEMS

2.1 The 340 ASCII characters in cipherPr2.1 result from a columnar tranposition using width N = 6 or 7 of plaintext from a sales brochure of TCC Incorporated, which markets equipment to secure network communications.

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                         cipherPr2.1
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utdacouzvpcinr erglltttfiia eruieycnCdpw se flSutsflgeknnowr
renrerguisronivaoie nern fma isl olnncfvrnOeergih emmD iea a
iao noeemcnub npos m.nomtst eT oeeofe-dMqne bis aet ppcuo dn
mtuacis rt cnevooe ocsraldte i eieeC mtnx yr e es i hdsima
e aye erosifihdcinuhae valf-tsi Cpsie,luyg.ehedtfteepocssbse
lnehei tntTe noc hgCe otcuryEi slehceat
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2.2 The 697 ASCII characters in cipherPr2.2 result from the columnar transposition ...