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Also known as: PCBC
A chaining mode where encryption errors propagate to subsequent blocks, historically used in Kerberos but rarely used today.
DESCRIPTION
Propagating Cipher-Block Chaining (PCBC) is a block cipher mode that combines both the previous ciphertext and plaintext blocks with the current plaintext before encryption. This design causes errors to propagate through subsequent blocks, an intentional property for certain detection goals. PCBC appeared historically in Kerberos v4 but has fallen out of favor due to complexities and security considerations. It is not standardized by NIST and is seldom recommended for modern systems. Where encountered in legacy contexts, careful handling and migration are advised.
ALTERNATIVE DEFINITIONS
Wikipedia
Propagating cipher-block chaining (PCBC) is a block cipher mode of operation that combines portions of the previous ciphertext block and the previous plaintext block with the current plaintext block before encryption.
Highlights the dual-dependence on previous ciphertext and plaintext blocks.
Handbook of Applied Cryptography
Propagating cipher-block chaining (PCBC) mode modifies the chaining so that errors in a ciphertext block affect the decryption of subsequent blocks.
Emphasizes error propagation property central to PCBC.
RELATED TERMS
Electronic Codebook Symmetric Block Cipher Algorithms Initialization Vector Padding Kerberos Mode of Operation Error Propagation Authentication Galois-Counter Mode
COMPETING TERMS
RELATIONS
- Broader: Cipher Block Chaining
KNOWLEDGE AREAS
Data Security Software Engineering
TARGET AUDIENCE
Security Architect Cybersecurity Engineer Software Developer
EXTERNAL SOURCES
- Wikipedia - Propagating cipher-block chaining
- Handbook of Applied Cryptography - Description and properties of PCBC mode
- MIT Kerberos - Historical context of PCBC in Kerberos
TOP QUESTIONS
Why was Propagating Cipher-Block Chaining used historically?
PCBC was used in early Kerberos to propagate errors as a form of tamper detection, but it introduced complexities and is now avoided.
Category: History
Is Propagating Cipher-Block Chaining secure for modern use?
It is not recommended. Modern AEAD modes offer better, well-understood security properties and simpler implementation requirements.
Category: Risks
How does PCBC differ from CBC?
PCBC mixes in parts of both previous plaintext and ciphertext, causing decryption errors to propagate more extensively than in CBC.
Category: Comparison
Where might I still encounter PCBC?
Mostly in legacy Kerberos v4 implementations or historical code; modern Kerberos no longer uses it.
Category: Usage
What is a competing term for PCBC?
CBC is the more common chaining mode historically; AEAD modes like GCM are preferred today.
Category: Alternatives
What are common mistakes with PCBC?
Assuming error propagation provides sufficient integrity; it does not replace proper authentication.
Category: Mistakes
How should PCBC be handled in legacy systems?
Support decryption for compatibility and plan migration to standardized, authenticated modes.
Category: Management
Does PCBC require an IV?
Yes, like CBC it requires an initialization vector for the first block.
Category: Definition
What is a simple analogy for PCBC?
A spill that keeps spreading; one error contaminates many subsequent blocks during decryption.
Category: Example