Transcriber's Note
Minor corrections, such as removing extra spaces or punctuation, or adding missing spaces or punctuation or diacritical marks, were made without note. Archaic and inconsistent spelling was retained. In two places, the number of a referenced figure was corrected. Grammar and spelling were only corrected as in the following list of notable changes.
In two places, “diagram” was corrected to “digram”.
In three places, “direct” was corrected to “directly”.
In [Chapter III], we italicized the first occurrence of “magic square” because it seemed like the author’s intention. In the same chapter, “said be clockwise” was corrected to “said to be clockwise”.
In [Figure 43], “ISGAY” was corrected to “ISGAU” to match previous figures and to correct spelling in the plaintext.
In [Chapter VII], “those who like method” was corrected to “those who like this method”.
In [Chapter XVIII], “misuse of the Type II slide” was corrected to “misuse of the Type I slide”.
In [Figure 139], “IQCIO” is corrected to “IQVIO”.
In the [Appendix], in the list of English trigrams, “WHI 51” was corrected to “WHI 71”.
Some corrections were made to the exercises in order to rectify the spelling in their plaintexts or (in one case) to resolve an inconsistency in its key.
In [exercise 33], seven letters were missing. The uncorrected cryptogram is VINSC FEAEO OHSEF HLEHU NSTNC LTSLC IAESH RHSIR ERMTS ETEPD TOINM RTTHT TLRUB E.
[Exercise 110]: “LRSFQ” corrected to “IRSFQ”.
[Exercise 115]: “FBEHZHWU” corrected to “FBEHZHWG”.
[Exercise 116]: “HVIYF” corrected to “HVXYF”.
[Exercise 128]: “JQAOJ” corrected to “JQAOI” and “QNUSG” to “QNUSU”.
[Exercise 130]: “FBWXJ” corrected to “FRWXJ”.
[Exercise 138]: “XVKFV” corrected to “XVKEV”.
[Exercise 141]: “KFTFB” corrected to “KFTFX”.
[Exercise 144]: “TAJNI WRDB” corrected to “TAJNW ARDB”.
[Exercise 145]: “TTHNY” corrected to “TTHNJ”.
[Exercise 146]: “PGOUR” corrected to “PGOUJ” and “VDDMH” to “VDDMP” (we are not sure about “VFCFT”).
[Exercise 147]: “UVSYC” corrected to “UBSYC”, “IXYDY” to “IXYPY”, “VXOOK” to “NXOOK”, and “NNHMM” to “NNHWM”.
[Exercise 149]: “MS” corrected to “PF”.
[Exercise 153]: “QY BN QM” corrected to “QY BM QM” and “BL PK QM” to “BL PO QM”.
[Exercise 40] has error(s) in the first 25 letters. We do not know what was the intention of its creator.
The above list should not be assumed to be correct or complete.
We wish to thank the anonymous proof-readers who volunteered at the British National Cipher Challenge (www.cipherchallenge.org).