Blind SQL Injection is a type of SQL injection attack where no error messages or data are directly returned to the attacker. Instead, the attacker sends specially crafted SQL queries that result in true or false responses.
Based on how the application responds (such as redirecting to a different page or loading time), the attacker infers information about the backend database.
According to CEH v13:
* Blind SQLi is used when standard SQL injection yields no visible output.
* It comes in two forms:
* Boolean-based: Infers information based on application behavior.
* Time-based: Infers information based on server response time delays.
Incorrect Options:
* A. Time-based SQLi is a sub-type of Blind SQLi, but the question describes Boolean-based behavior.
* B. Union SQL injection uses the UNION keyword to fetch additional rows; requires visible output.
* C. Error-based SQL injection relies on database error messages.
Reference - CEH v13 Official Courseware:
Module 14: Hacking Web Applications
Section: "Types of SQL Injection"
Subsection: "Blind SQL Injection (Boolean and Time-Based)"

The correct answer is RSA. CEH cryptography coverage describes RSA as a widely used asymmetric algorithm that supports encryption and digital signatures and is commonly deployed in public-key infrastructures. The question states that the transaction data is hashed, the hash is signed with the sender's private key, and the recipient verifies the signature with the matching public key. That is the classic RSA signature model presented in CEH materials. The additional clue is that the same algorithm is said to support encryption, digital signatures, and secure communications use cases. Diffie-Hellman is mainly a key exchange mechanism and is not used for digital signatures in the way described here. DSA is designed for digital signatures, but not for general encryption. ElGamal can support encryption and signatures, but CEH exam framing most strongly associates this full combination of encryption plus digital-signature verification with RSA. CEH references repeatedly emphasize RSA as the standard asymmetric cryptosystem for confidentiality, authentication, integrity, and nonrepudiation in enterprise communications. Because the described implementation combines hashing, private-key signing, and public-key verification within a broad asymmetric framework, RSA is the most accurate answer.

The CEH v13 content explains that stealth scanning involves modifying scan timing parameters to reduce packet frequency, randomize intervals, and avoid recognizable patterns typically flagged by intrusion detection systems. Slow, randomized timing-often achieved with Nmap's T0 or T1 timing templates- prevents bursts of traffic and allows scans to blend into normal network noise. IDS/IPS systems tuned for high-volume events may fail to detect such gradual reconnaissance. Fast SYN scans generate distinctive patterns easily identified by security monitoring tools. UDP scans, especially across all ports, produce high traffic volume and are extremely noisy. Xmas scans, although sometimes used for stealth against stateless filters, are still signature-detectable and inappropriate when stealth over time is required. Therefore, applying slow, randomized timing options aligns with CEH-approved reconnaissance techniques for evading detection while enumerating open ports.