712-50 Question 335
Single answerA CCISO is reviewing a proposed secure document-sharing process for the board of directors. The business requirement is that sensitive acquisition documents sent over the internet must remain confidential, recipients must be able to verify the sender's identity, and the organization must be able to scale trust management across external law firms without manually exchanging keys for each user. One architect proposes embedding the documents inside image files to avoid detection by attackers, while another proposes using digital certificates within a PKI-enabled solution. Which option is the MOST appropriate recommendation?
- A
Use steganography to hide the documents inside image files, because concealment provides both confidentiality and sender authentication without needing certificate management.
- B
Use symmetric encryption with a shared password for all law firms, because this simplifies key distribution and provides nonrepudiation if the password is controlled by the legal department.
- C
Use a PKI-based approach in which each sender and recipient has a digital certificate; encrypt documents for recipients using their public keys and use the sender's private key to digitally sign the documents.
- D
Use hashing alone for the documents before transmission, because hashes prove integrity and can be reversed by authorized recipients when needed.
Show answer and explanation
Correct answer: C
Explanation
The scenario requires confidentiality, sender verification, and scalable trust management across multiple external organizations. PKI is specifically designed to solve these problems by binding identities to public keys through digital certificates issued by trusted certificate authorities. In practice, confidentiality is achieved by encrypting data using the recipient's public key or, more commonly at scale, by encrypting the document with a symmetric session key and then protecting that key with the recipient's public key. Authentication, integrity, and nonrepudiation are supported through digital signatures created with the sender's private key and verified with the sender's public key in the certificate. Steganography differs from cryptography: steganography hides the presence of information, while cryptography transforms information to protect its confidentiality and can also support integrity, authentication, and nonrepudiation when used with digital signatures. Relevant best-practice references include NIST guidance on public key infrastructure and digital signatures, including NIST SP 800-32 on PKI and NIST FIPS 186 for digital signature standards, as well as established X.509 certificate practices used in enterprise trust models.
- A. Incorrect.
Incorrect. Steganography is the practice of concealing the existence of information, not a substitute for cryptography. Hiding documents in images may reduce visibility, but it does not inherently provide strong confidentiality, identity assurance, integrity, or scalable trust. A recipient also cannot reliably verify the sender's identity through steganography alone. This option reflects a common misconception that hidden data is equivalent to encrypted data.
- B. Incorrect.
Incorrect. Symmetric encryption can provide confidentiality, but using a single shared password across multiple external firms creates major key management and accountability problems. It does not provide true nonrepudiation, because anyone with the shared secret could have encrypted or accessed the document. Shared secrets do not scale well across many external parties and increase the impact of compromise. This choice confuses confidentiality with identity assurance and nonrepudiation.
- C. Correct.
Correct. A PKI-based model is the best fit for the stated business requirements. Encrypting with the recipient's public key helps protect confidentiality so only the holder of the corresponding private key can decrypt. Digitally signing with the sender's private key allows recipients to validate the signature using the sender's public key in the digital certificate, supporting authentication, integrity, and nonrepudiation. Digital certificates issued by trusted certificate authorities enable scalable trust relationships with external firms without manually exchanging keys one by one.
- D. Incorrect.
Incorrect. Hashing provides a one-way integrity check, not confidentiality. A cryptographic hash cannot be reversed by authorized recipients to recover the original document. This option demonstrates a common misunderstanding between hashing and encryption/decryption. While hashes are useful as part of digital signatures or integrity verification, hashing alone does not satisfy the requirement to protect sensitive content in transit.