Crypto U4, Block Cipher, Electronic Codebook Mode (ECB)

Encryption

• key used with encryption algorithm to encrypt each block of plaintext

Decryption

• key used with decryption algorithm to decrypt each block of plaintext

Problems

• Attacker could reorganize order of blocks of text without noticing.

• Attacker could replay old parts of message.

• Attacker could delete blocks of ciphertext without noticing.

• Attacker could repeated blocks without noticing.

• Attacker could mount dictionary attacks.

• Attacker could mount statistical attacks since the same key is used to encrypt multiple blocks.

How could we improve it?

• increase the size of the plaintext bllocks and cipher alphabets (combat dictionary attacks)

• allow some plaintext letters to be encrypted to different ciphertext letters

• make the ciphertext encryption position dependent