Hill Cipher (2×2)
Matrix-based classical cipher with a 2×2 key matrix mod 26.
Valid key matrix. det = 9 ≡ 9 (mod 26), coprime with 26.
About this tool
Encrypt or decrypt with a 2×2 integer matrix [[a,b],[c,d]] mod 26. Decryption requires the matrix to be invertible mod 26.