CVE-2004-2721 in Openskat
Summary
by MITRE
The CheckGroup function in openSkat VTMF before 2.1 generates public key pairs in which the "p" variable might not be prime, which allows remote attackers to determine the private key and decrypt messages.
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Analysis
by VulDB Data Team • 03/10/2015
The vulnerability described in CVE-2004-2721 affects the openSkat VTMF software version 2.1 and earlier, specifically within the CheckGroup function responsible for generating public key pairs. This flaw represents a critical weakness in the cryptographic implementation that directly impacts the security of encrypted communications. The vulnerability stems from the improper generation of cryptographic parameters where the "p" variable, a crucial component in the mathematical foundation of the encryption scheme, may not actually be a prime number as required by cryptographic standards.
The technical flaw occurs when the CheckGroup function fails to properly validate that the generated parameter "p" meets the mathematical requirements for prime numbers. In cryptographic systems, particularly those based on discrete logarithm problems, the security relies heavily on the difficulty of solving mathematical problems involving large prime numbers. When "p" is not prime, the mathematical structure becomes compromised, creating vulnerabilities that attackers can exploit to reverse-engineer the private key components. This weakness directly violates the fundamental principles of public key cryptography as outlined in standards such as FIPS 186-4 and ISO/IEC 14888-3, which mandate proper prime number generation for cryptographic security.
The operational impact of this vulnerability is severe as it allows remote attackers to completely compromise the encryption system. Once an attacker successfully determines that the "p" parameter is not prime, they can use mathematical techniques to factor the modulus and subsequently derive the private key. This compromise enables attackers to decrypt messages that were previously protected by the system, effectively nullifying the confidentiality guarantees provided by the encryption. The vulnerability affects any communication that relies on the compromised key generation process, potentially exposing sensitive data including personal information, financial records, and proprietary communications. The attack can be executed remotely without requiring local access or special privileges, making it particularly dangerous in networked environments.
Mitigation strategies for this vulnerability require immediate patching of the openSkat VTMF software to version 2.1 or later where the CheckGroup function has been properly implemented with correct prime number validation. Organizations should also conduct thorough audits of all cryptographic implementations to ensure that prime number generation follows established standards and includes proper validation routines. The fix should implement rigorous primality testing using algorithms such as Miller-Rabin or deterministic tests for smaller numbers to ensure that "p" values meet cryptographic requirements. Additionally, system administrators should consider implementing cryptographic key rotation procedures to replace any compromised keys that may have been generated prior to the fix. This vulnerability aligns with CWE-327 (Use of a Broken or Risky Cryptographic Algorithm) and represents a classic example of how improper implementation of cryptographic primitives can lead to complete system compromise, as documented in various ATT&CK techniques related to cryptographic attacks and credential access.