Cryptanalysis of Caesar ●●●●● ●●●● ●●0 Cipher ●●● ●●●● o There are only 25 possible ciphers A maps to B,.., Z o Attacker could simply try each in turn ● a brute- force search o given ciphertext, just try all shifts of letters o do need to recognize when have plaintext E.g. break ciphertext GCUA VQ DTGCM e Caesar cipher is far from secure! COMP4690. HKBUCOMP4690, HKBU 12 Cryptanalysis of Caesar Cipher ⚫ There are only 25 possible ciphers ⚫ A maps to B,…,Z ⚫ Attacker could simply try each in turn ⚫ a brute-force search ⚫ given ciphertext, just try all shifts of letters ⚫ do need to recognize when have plaintext ⚫ E.g. break ciphertext "GCUA VQ DTGCM“ ⚫ Caesar cipher is far from secure!