The correct answers are A, D, and E. In IPsec VPN terminology, DES, 3DES, and AES are encryption algorithms used to provide confidentiality for protected IP traffic. Juniper’s IPsec material identifies AES, DES, and Triple DES/3DES as IPsec encryption standards, while separating them from authentication hash algorithms such as MD5, SHA-1, and SHA-2. This distinction matters heavily in JNCIS-SEC because IPsec proposals contain different cryptographic functions: encryption protects packet confidentiality, while authentication/hash algorithms validate integrity and origin.
Option B, SHA-1, is incorrect because SHA-1 is a hashing/authentication algorithm, not an encryption algorithm. It produces a message digest used for integrity checking and authentication, commonly as an HMAC variant. Option C, MD5, is also incorrect for the same reason: MD5 is a message-digest algorithm used for authentication/integrity, not for encrypting payload data. AES is the modern preferred encryption family because it is cryptographically stronger than DES and 3DES at comparable key strengths, while DES and 3DES remain historically recognized IPsec encryption algorithms. Reference topics: IPsec VPN, IPsec proposals, encryption algorithms, authentication algorithms, DES, 3DES, AES, SHA, and MD5.