312-50V10 · Question #325
Diffie-Hellman (DH) groups determine the strength of the key used in the key exchange process. Which of the following is the correct bit size of the Diffie-Hellman (DH) group 5?
The correct answer is C. 1536 bit key. Diffie-Hellman Group 5 is standardized with a 1536-bit modulus, placing it between the weaker Groups 1 and 2 and the stronger Group 14.
Question
Diffie-Hellman (DH) groups determine the strength of the key used in the key exchange process. Which of the following is the correct bit size of the Diffie-Hellman (DH) group 5?
Options
- A768 bit key
- B1025 bit key
- C1536 bit key
- D2048 bit key
How the community answered
(22 responses)- A5% (1)
- C91% (20)
- D5% (1)
Why each option
Diffie-Hellman Group 5 is standardized with a 1536-bit modulus, placing it between the weaker Groups 1 and 2 and the stronger Group 14.
768-bit is the key size for DH Group 1, which is considered cryptographically weak and deprecated, not Group 5.
1025-bit is not a standardized key size for any defined DH group and does not correspond to any RFC-defined group.
Per RFC 3526, DH Group 5 is defined with a 1536-bit prime modulus. The DH group hierarchy progresses as Group 1 at 768-bit, Group 2 at 1024-bit, Group 5 at 1536-bit, and Group 14 at 2048-bit, making 1536-bit the precise and standardized key size for Group 5.
2048-bit corresponds to DH Group 14 as defined in RFC 3526, not Group 5.
Concept tested: Diffie-Hellman group key sizes and standards
Source: https://www.rfc-editor.org/rfc/rfc3526
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