Letter Frequency Analysis in Cryptograms (ETAOIN SHRDLU)
Letter frequency analysis is the foundational weapon of cryptanalysis. In standard English, letters do not occur with equal probability. Instead, a tiny fraction of the alphabet dominates written text.
The ETAOIN SHRDLU Hierarchy
The letter E is by far the most frequent in English (~12.7%), followed closely by T (~9.1%), A (~8.2%), O (~7.5%), I (~7.0%), and N (~6.7%). Together, these six letters comprise almost 50% of any typical English passage. When tackling an Aristocrat cryptogram, tally all letter occurrences and test the top cipher characters against E, T, and A.
Common Digraphs and Recurring Pairs
Two-letter combinations (digraphs) provide immense leverage. The most frequent English digraphs are TH, HE, IN, ER, AN, RE, ED, ON, ES, and ST. When you identify the cipher letter representing E, look for the letter immediately preceding it—that character has an exceptionally high probability of being H (forming HE or THE).
Vowel Spotting vs Consonant Clusters
Vowels (A, E, I, O, U) rarely appear consecutively in large clusters in English, but they touch nearly every consonant. By analyzing letter contacts (which letters appear directly adjacent to many different characters), you can separate the vowels from low-contact consonants.
Put This Strategy Into Practice
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