Paraphrasing Daniel Olsen, Cryptanalysis for the FBI:
- 340-cipher is similar to the 408-cipher except that the 340-cipher appears to have "bogus rows."
- Lines 1-3 and 11-13 have distinctly greater degrees of randomness.
- Lines 4, 10, 14, 17 and 18 have high character repetition.
- Rows are more random than columns.
- Most likely a homophonic substitution.