SY0-701 Question 118
Select 2Cryptographic attacks: Downgrade , Collision , BirthdayA company signs software update packages with a legacy certificate that uses SHA-1. During a security review, the team learns that attackers may be able to create two different files that produce the same hash and potentially abuse trust in the signed package. At the same time, packet captures show some remote clients can be manipulated during connection setup to fall back from TLS 1.3 to TLS 1.0 when a man-in-the-middle device interferes with negotiation. Which TWO issues best describe these findings?
- A
A collision attack against the SHA-1-based signing process
- B
A birthday attack exploiting the reduced work needed to find matching hashes
- C
A downgrade attack against the TLS session negotiation
- D
A replay attack against the signed update package
- E
A pass-the-hash attack against the client authentication process
Show answer and explanation
Correct answers: A, C
Explanation
The two findings map to two different cryptographic attack categories. First, using SHA-1 for software signing raises collision concerns. A collision attack means two distinct inputs produce the same hash value, which is especially dangerous for digital signatures and integrity checks. The birthday paradox explains why finding any two matching hashes is significantly easier than finding a preimage, which is why weak hashes such as SHA-1 are no longer recommended for collision-resistant use. Second, forcing a connection to fall back from TLS 1.3 to TLS 1.0 is a downgrade attack because the attacker manipulates negotiation to use a weaker protocol. Best practice is to disable deprecated protocols and weak hash algorithms, and to use modern configurations aligned with current guidance such as NIST recommendations to transition away from SHA-1 for digital signatures and to prefer current versions of TLS.
- A. Correct.
Correct. A collision attack occurs when an attacker finds two different inputs that produce the same hash output. In this scenario, the concern is that SHA-1 is weak enough that an attacker may craft two different files with the same digest, undermining confidence in a signature workflow that relies on that hash. This matches the described risk to signed software packages.
- B. Incorrect.
Incorrect. A birthday attack is the mathematical strategy that leverages the birthday paradox to make collisions easier to find than brute-forcing a specific hash value. It explains why collisions become practical in weaker hash algorithms, but the issue described in the software-signing scenario is specifically a collision attack. On Security+ exams, the practical event being identified here is the collision itself, while the birthday concept is the underlying principle that makes such attacks feasible.
- C. Correct.
Correct. A downgrade attack occurs when an attacker forces communicating parties to use a weaker protocol, cipher suite, or version than they would normally use. Interfering with negotiation so clients fall back from TLS 1.3 to TLS 1.0 is a textbook example of a downgrade attack because it reduces the security of the connection.
- D. Incorrect.
Incorrect. A replay attack involves capturing valid data transmission and retransmitting it later to gain unauthorized effects. The scenario does not describe reuse of a captured signed package transmission or session data; it describes hash weakness and forced protocol fallback instead.
- E. Incorrect.
Incorrect. Pass-the-hash is an authentication attack in which an attacker uses a stolen password hash to authenticate without knowing the plaintext password, typically in certain enterprise authentication contexts. The scenario is about digital signatures and TLS negotiation, not lateral movement using credential hashes.