CVE-2005-1797 in OpenSSL
Summary
by MITRE
The design of Advanced Encryption Standard (AES), aka Rijndael, allows remote attackers to recover AES keys via timing attacks on S-box lookups, which are difficult to perform in constant time in AES implementations.
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Analysis
by VulDB Data Team • 07/05/2021
The vulnerability described in CVE-2005-1797 represents a critical side-channel attack vector targeting the Advanced Encryption Standard algorithm that was widely adopted as a cryptographic primitive for securing sensitive data. This flaw specifically exploits the implementation weaknesses in how AES handles its substitution box operations, which are fundamental components of the encryption process. The vulnerability affects implementations that do not properly account for timing variations during the execution of S-box lookups, creating opportunities for attackers to infer cryptographic key material through careful analysis of execution time variations.
The technical implementation flaw stems from the fact that AES uses a substitution layer called the S-box, which maps input bytes to output bytes using a specific mathematical transformation. When implementations of AES do not execute these S-box lookups in constant time, variations in execution speed can reveal information about the secret key being processed. Attackers can perform timing analysis by measuring the time differences between different encryption operations, particularly when the S-box lookup depends on the key material. This approach follows the established pattern of timing attacks that have been documented in cryptographic literature since the early 1990s, where temporal variations in computation can expose secret information.
The operational impact of this vulnerability extends far beyond simple cryptographic weakness, as it affects the fundamental security assumptions of systems relying on AES encryption. Any system implementing AES without proper constant-time execution measures becomes susceptible to key recovery attacks that can compromise encrypted data confidentiality. The attack is particularly concerning because it requires no direct access to the encryption process or the cryptographic keys themselves, but rather relies on observing and analyzing timing variations from external network traffic or system monitoring. This makes the vulnerability particularly dangerous in environments where attackers have access to performance monitoring tools or can conduct controlled timing experiments against the target system.
Mitigation strategies for this vulnerability require implementing constant-time algorithms that ensure all execution paths take identical amounts of time regardless of the input data or key values. The most effective approach involves reworking the S-box lookup implementations to avoid conditional branches or memory access patterns that vary based on key material. Cryptographic libraries and implementations must adopt techniques such as table lookups that do not depend on secret values, or employ masked implementations that obscure timing variations. Industry standards such as NIST SP 800-38B provide guidelines for implementing AES in a manner that resists side-channel attacks, while the CWE catalog categorizes this issue under CWE-203, specifically addressing "Observable Timing Discrepancy." The ATT&CK framework recognizes this as a form of information leakage through side channels, specifically under the technique of "Timing Attack" which targets the temporal characteristics of cryptographic implementations. Organizations should conduct thorough code reviews and implement continuous monitoring to detect and prevent such timing variations in cryptographic operations.