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PKCS#7

PKCS#7 padding scheme where padding bytes contain the number of padding bytes added. This ensures data is padded to block boundary with deterministic padding removal. It is the most widely used padding scheme for block ciphers and supports variable block sizes from 1 to 255 bytes.

Properties

Property	Value
Category	Padding Schemes
Sub-category	Block Padding
Security status	🛡️ Secure
Complexity	Not specified
Inventor	RSA Laboratories
Year	1993
Origin	🇺🇸 United States
Source	algorithms/padding/pkcs.js

Capabilities

Flag	Value
IsLengthIncluded	No

Security

Status: 🛡️ Secure

Known vulnerabilities

Issue	Description	Mitigation
Padding Oracle Attack	When decryption errors reveal padding validity, attackers can decrypt arbitrary ciphertexts byte by byte. Use authenticated encryption modes or ensure error messages don’t distinguish between padding and other decryption errors.	—
Length Disclosure	The padding scheme reveals information about the original message length modulo block size.	—

Documentation

• RFC 2315 - PKCS #7
• RFC 5652 - CMS
• Padding in Cryptography

References

• OpenSSL PKCS7 Padding
• Crypto++ PKCS Padding
• RSA Laboratories

Test vectors

3 vectors ship with this algorithm and run in the test suite. Byte values are hexadecimal.

Vector 1 — PKCS#7 padding with 17 bytes needed

Source: RFC 2315

Field	Value
blockSize	32
input	6bc1bee22e409f96e93d7e11739317
expected	6bc1bee22e409f96e93d7e117393171111111111111111111111111111111111

Vector 2 — PKCS#7 padding for full block

Source: RFC 2315

Field	Value
blockSize	32
input	6bc1bee22e409f96e93d7e117393172a
expected	6bc1bee22e409f96e93d7e117393172a10101010101010101010101010101010

Vector 3 — PKCS#7 padding with 3 bytes needed

Source: RFC 2315

Field	Value
blockSize	8
input	6bc1bee22e
expected	6bc1bee22e030303

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