PKCS#7 padding
PKCS#7 padding is a byte-padding scheme in which each appended byte contains the number of padding bytes added to complete a block.
Hacking Cryptography
PKCS#7 padding is a byte-padding scheme in which each padding byte contains the number of padding bytes added to complete a block.
- How it is used
- Fits plaintext to block-cipher boundaries before encryption and supports unpadding after decryption.
- How deep it goes
- Defines the byte rule, exact-block behavior, construction, removal, validation, and padding-oracle consequence.
- Examples
- Uses repeated 0x04 bytes, Go padding functions, and an AES-CBC encrypted-timestamp server.
- What you can do after
- Build it from scratch with padding, removal, and validation routines while avoiding distinguishable padding errors.
Real-World Cryptography
PKCS#7 padding appends bytes whose values equal the number of padding bytes required to reach a block boundary.
- How it is used
- Prepares plaintext for block encryption by extending it to a complete block boundary.
- How deep it goes
- Explains the padding rule, full-block case, reversibility, and unpadding procedure, but not implementation details.
- Examples
- Uses eight-byte plaintext padded with eight bytes of value 8, plus a full sixteen-byte padding block.
- What you can do after
- Apply it when preparing and reversing block-cipher plaintext, including messages already aligned to a block.
Related concepts
- paddingkind of · Padding is the addition of extra space, values, or data around or within a structure to satisfy size, alignment, layout, or processing requirements.
- AESused by · AES is a standardized symmetric block cipher that encrypts and decrypts data in 128-bit blocks using 128-, 192-, or 256-bit keys.
- encryptionconfigures · Encryption is the cryptographic transformation of readable data into ciphertext to conceal its contents, reversible through decryption with appropriate information.
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