nullpadding

Null padding, also known as zero padding, is a simple padding method used to fill a data block to a required size by appending zero-valued bytes (0x00). It is commonly applied in block cipher schemes where the input must be a multiple of the block size; the last block is extended with as many 0x00 bytes as needed to reach the next multiple.

Removal of padding after decryption involves discarding trailing zero bytes. However, null padding is ambiguous if the original plaintext ends with zero-valued bytes, since the receiver cannot always distinguish which zeros are padding and which are data.

Security and reliability considerations are important. Null padding does not provide intrinsic secrecy or integrity guarantees and can leak information about message length. It can be vulnerable to padding oracle attacks if padding validity is leaked through error messages or timing side channels. For modern cryptographic practice, more robust padding schemes such as PKCS#5/PKCS#7, or the use of authenticated encryption modes that do not require padding, are typically preferred.

Usage notes: Null padding is sometimes encountered in legacy systems or specific environments where the data format guarantees that padding will not be mistaken for data, or where the message lengths are managed externally. In many contemporary applications, it has fallen out of favor due to the ambiguity it introduces and is generally replaced by more robust padding schemes or by padding-free authenticated encryption.

See also: padding schemes, PKCS padding, padding oracle, block ciphers, authenticated encryption.