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Difficulty: MediumPublic Key Infrastructure and Certificate Management

An enterprise security administrator is establishing a Public Key Infrastructure (PKI) key lifecycle policy for employee S/MIME email certificates. The policy specifies that private keys associated with email encryption certificates must be backed up to a key escrow agent, whereas private keys associated with digital signature certificates are strictly prohibited from key escrow. Which of the following best explains the security rationale for prohibiting key escrow on digital signature private keys?

  1. Escrowing signature private keys violates non-repudiation because authorized escrow administrators could technically forge a user's digital signature.Answer
  2. B
    Escrowing signature private keys prevents receiving clients from validating message integrity using hashing algorithms.
  3. C
    Signature private keys must be generated directly by the Certificate Authority during the Certificate Signing Request lifecycle rather than locally.
  4. D
    Digital signatures rely exclusively on symmetric encryption algorithms, which are mathematically incompatible with asymmetric key escrow vaults.

Answer

Escrowing signature private keys violates non-repudiation because authorized escrow administrators could technically forge a user's digital signature.
Digital signatures guarantee non-repudiation, which requires sole control over the signing private key. Archiving or escrowing a signature private key means another party (such as a system administrator or key recovery agent) could potentially use that key to sign documents or emails, thereby destroying the legal proof of non-repudiation.

Step-by-Step Solution

1
Analyze the dual-key requirement in PKI deployment for S/MIME.
S/MIME uses two distinct key pairs: one pair for bulk data encryption/decryption and one pair for digital signatures.
Encryption keys require backup/escrow to recover encrypted business data if an employee leaves or loses access. Signature keys serve a different security purpose.
2
Evaluate the impact of key escrow on the security properties of digital signatures.
Digital signatures guarantee authenticity, integrity, and non-repudiation.
Non-repudiation mandates that only the single private key owner could have signed the document. If any third party or escrow agent has access to the private key, the owner can plausibly claim someone else signed it.

Key Concept

Key Escrow vs. Non-Repudiation in PKI Dual-Key Management
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Topics

Public Key Infrastructure and Certificate Management

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