## 7.4 CRIBBING RED CIPHERTEXT

We will describe the cryptanalysis of RED ciphertext using English-language text. The *vowel/consonant pattern* of a (plaintext) crib *u* = (*u*_{0}, *u*_{1}, …, *u*_{M − 1}) is

**TABLE 7.8 Normalized ***κ*-Values for Example 7.4

A *necessary* condition that the RED ciphertext fragment *y*_{[i,i+M)} ≡ (*y*_{i},…, *y*_{i+M−1}) be the encipherment of the (plaintext) crib *u* = (*u*_{0}, *u*_{1}, …, *u*_{M−1}) is

To crib RED ciphertext for the plaintext *u* = (*u*_{0}, *u*_{1}, …, *u*_{M−1}), the RED ciphertext is searched for fragments *y*_{[i,i+M)} that have the same the vowel/consonant pattern as that of *u.*

Of course, Equation (7.17) is only a necessary condition that *u* → *y*_{[i,i+M)} and some fragments fail to correspond to plaintext crib. Additional constraints need to be imposed before concluding that *y*_{[i,i+M)} is the encipherment of the crib *u.*

### 7.4.1 Cribbing RED Cipherment: No Inactive Breakwheel Pins

If all pins on the breakwheel are active, then *τ* = 47 and *P*(*i*) = *P*(0) + *i*. As *P*(0) is unknown, the recovery of *θ*_{V} and *θ*_{C} by cryptanalysis assuming *P*(0) = 0 will then be related to Tables 7.5 and 7.6 by a shift in rows.

If *y*_{[i,i+M)} = (*y*_{i}, y_{i} _{+ 1}, …, *y*_{i + M−1}) is the RED encipherment of the crib *u* = (*u*_{0}, *u*_{1}, …, *u*_{M−1}), then Equations (7.11 ...