Publication

CBC Padding: Security Flaws in SSL, IPSEC, WTLS, ...

Serge Vaudenay
2001
Reports

Abstract

In many standards, e.g. SSL/TLS, IPSEC, WTLS, messages are first pre-formatted, then encrypted in CBC mode with a block cipher. Decryption needs to check if the format is valid. Validity of the format is easily leaked out from communication protocols because the receiver usually sends an error message when the format is not valid. This is a side channel. In this paper we show that the validity of the format of the decryption is actually a hard core bit predicate. We demonstrate this by implementing an efficient and practical side channel attack which enables the decryption of any ciphertext. The attack complexity is O(NbW) where N is the message length in blocks, b is the block length in words, and W is the number of possible words (typically 256). We also discuss about extensions to other padding schemes and various ways to fix the problem.

Official source

https://infoscience.epfl.ch/entities/publication/86db2ecf-613f-4aa7-a090-582d4291f318

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Serge Vaudenay
2001
Reports

Abstract

Official source

https://infoscience.epfl.ch/entities/publication/86db2ecf-613f-4aa7-a090-582d4291f318

About this result

Related concepts (32)

Block cipher

In cryptography, a block cipher is a deterministic algorithm that operates on fixed-length groups of bits, called blocks. Block ciphers are the elementary building blocks of many cryptographic protocols. They are ubiquitous in the storage and exchange of data, where such data is secured and authenticated via encryption. A block cipher uses blocks as an unvarying transformation. Even a secure block cipher is suitable for the encryption of only a single block of data at a time, using a fixed key.

Transport Layer Security

Transport Layer Security (TLS) is a cryptographic protocol designed to provide communications security over a computer network. The protocol is widely used in applications such as email, instant messaging, and voice over IP, but its use in securing HTTPS remains the most publicly visible. The TLS protocol aims primarily to provide security, including privacy (confidentiality), integrity, and authenticity through the use of cryptography, such as the use of certificates, between two or more communicating computer applications.

Communication protocol

A communication protocol is a system of rules that allows two or more entities of a communications system to transmit information via any variation of a physical quantity. The protocol defines the rules, syntax, semantics, and synchronization of communication and possible error recovery methods. Protocols may be implemented by hardware, software, or a combination of both. Communicating systems use well-defined formats for exchanging various messages.

Related publications (1)

CBC Padding: Security Flaws in SSL, IPSEC, WTLS, ...

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