CVE-2014-3591

What it actually does

Absence of ciphertext blinding during ElGamal decryption in Libgcrypt and GnuPG permits recovery of the private key by measuring electromagnetic emanations produced during modular multiplication of attacker-supplied ciphertexts.

Why it matters to the business

Organizations relying on GnuPG or Libgcrypt for long-term key protection face risk of private-key theft when an attacker obtains brief physical proximity to decryption hardware, potentially exposing all past and future encrypted data or signatures.

How an attack unfolds

An attacker with physical access crafts special ElGamal ciphertexts and records fluctuations in the electromagnetic field emitted by the CPU while multiplication occurs; statistical analysis of the traces factors the ciphertext and reconstructs the private key without software interaction.

How to fix it

Upgrade Libgcrypt to 1.6.3 or later and GnuPG to 1.4.19 or later on all affected systems; re-generate any ElGamal keys that may have been used on unpatched versions.

How to confirm the fix worked

Inventory all installations of libgcrypt and gnupg, confirm versions meet or exceed 1.6.3 and 1.4.19 respectively, and verify that ElGamal key-generation or decryption operations now include blinding by code review or vendor-supplied test vectors.

Typical attack path

1. Gain brief physical proximity to a system performing ElGamal decryption
2. Trigger or observe decryption of attacker-controlled ciphertexts
3. Capture high-resolution EM traces during modular multiplication
4. Process traces offline to factor the ciphertext and extract the private key

How to detect it

Monitor physical-access logs, badge records, and hardware tamper sensors for unexplained proximity to decryption systems; after suspected exposure, look for sudden use of the compromised private key in unexpected locations or network traffic.

What your security team should do

• Immediately apply available updates for libgcrypt and gnupg across the environment
• Replace any ElGamal keys that performed decryption on unpatched versions
• Restrict physical access to systems that handle long-term private keys
• Audit cryptographic library versions as part of routine asset management