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Bit Padding

Bit padding scheme appends a single ‘1’ bit (0x80 byte) followed by zero bits to fill the block. This method provides unambiguous padding removal and is commonly used in hash functions and cryptographic protocols. Also known as ISO/IEC 7816-4 padding.

Properties

Property	Value
Category	Padding Schemes
Sub-category	Bit Padding
Security status	🛡️ Secure
Complexity	Not specified
Inventor	Merkle-Damgård
Year	1979
Origin	Not specified
Source	algorithms/padding/bit-padding.js

Capabilities

Flag	Value
IsLengthIncluded	No

Security

Status: 🛡️ Secure

Known vulnerabilities

Issue	Description	Mitigation
None Known	Bit padding provides unambiguous padding removal with no known cryptographic weaknesses.	—
Length Expansion	Always adds at least one byte of padding, which may be undesirable for some applications.	—

Documentation

• Merkle-Damgård Construction
• ISO/IEC 7816-4
• Padding in Cryptography

References

• Hash Function Design
• Smart Card Standards
• Cryptographic Padding Methods

Test vectors

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

Vector 1 — Bit padding with 17 bytes needed

Source: ISO/IEC 7816-4

Field	Value
blockSize	32
input	6bc1bee22e409f96e93d7e11739317
expected	6bc1bee22e409f96e93d7e117393178000000000000000000000000000000000

Vector 2 — Bit padding for full block

Source: ISO/IEC 7816-4

Field	Value
blockSize	32
input	6bc1bee22e409f96e93d7e117393172a
expected	6bc1bee22e409f96e93d7e117393172a80000000000000000000000000000000

Vector 3 — Bit padding with 3 bytes needed

Source: ISO/IEC 7816-4

Field	Value
blockSize	8
input	6bc1bee22e
expected	6bc1bee22e800000

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