CVE-2011-1945 in OpenSSL
Summary
by MITRE
The elliptic curve cryptography (ECC) subsystem in OpenSSL 1.0.0d and earlier, when the Elliptic Curve Digital Signature Algorithm (ECDSA) is used for the ECDHE_ECDSA cipher suite, does not properly implement curves over binary fields, which makes it easier for context-dependent attackers to determine private keys via a timing attack and a lattice calculation.
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Analysis
by VulDB Data Team • 08/05/2024
The vulnerability described in CVE-2011-1945 represents a critical weakness in the cryptographic implementation of OpenSSL's elliptic curve cryptography subsystem. This flaw specifically affects versions 1.0.0d and earlier, where the implementation of elliptic curve digital signature algorithm (ECDSA) within the ECDHE_ECDSA cipher suite demonstrates improper handling of curves over binary fields. The vulnerability arises from insufficient cryptographic implementation practices that fail to properly address the mathematical complexities inherent in binary field elliptic curve operations, creating exploitable timing variations in the cryptographic processing.
The technical implementation flaw stems from the lack of constant-time execution in the ECC signature generation process when operating over binary fields. Attackers can exploit this timing variation through sophisticated lattice-based mathematical calculations to reconstruct private keys from public information. This type of attack represents a classic side-channel vulnerability where the timing characteristics of cryptographic operations leak information about the underlying secret values. The vulnerability specifically impacts the ECDHE_ECDSA cipher suite, which combines elliptic curve Diffie-Hellman key exchange with ECDSA signatures, making it particularly dangerous for secure communications that rely on this cryptographic combination.
The operational impact of this vulnerability extends beyond simple key compromise, as it enables context-dependent attackers to perform sophisticated cryptanalysis that can undermine the entire security foundation of systems using affected OpenSSL versions. The timing attack approach allows adversaries to gather sufficient information through repeated measurements of cryptographic operation durations, combined with lattice reduction techniques to solve the underlying mathematical problems that reveal private key components. This vulnerability affects any system that implements the ECDHE_ECDSA cipher suite using OpenSSL versions prior to 1.0.0e, potentially compromising the confidentiality and integrity of encrypted communications, digital signatures, and authentication mechanisms that depend on elliptic curve cryptography.
Security mitigations for this vulnerability primarily involve upgrading to OpenSSL version 1.0.0e or later, which includes proper constant-time implementations for binary field operations and addresses the timing variations that enable the attack. Organizations should also consider implementing additional cryptographic safeguards such as using curves over prime fields instead of binary fields where possible, as prime field implementations typically provide better resistance to timing attacks. The vulnerability aligns with CWE-310, which addresses cryptographic weaknesses, and represents a specific instance of timing side-channel attacks that fall under ATT&CK technique T1552.004, focusing on credentials from password storage. System administrators should conduct comprehensive audits of all systems using affected OpenSSL versions and implement immediate patches to prevent exploitation, as the vulnerability can be leveraged by attackers with minimal privileges to compromise the security of encrypted communications and digital signatures.