Question 1

What is hash lookup?

Accepted Answer

Hash lookup searches hash values (MD5, SHA-1, SHA-256) in databases of known hashes from data breaches, malware samples, or password dictionaries. Used to identify compromised passwords, detect malware files, or verify file integrity. Compares unknown hash against millions of known values. Faster than brute-force cracking. Common in incident response and security research.

Question 2

Which hash databases are available?

Accepted Answer

Popular databases: Have I Been Pwned (850M+ password hashes), VirusTotal (malware file hashes), NSRL (National Software Reference Library), MD5decrypt, CrackStation (15B+ hashes), HashKiller. Some free, others paid/API. HIBP uses k-anonymity (sends first 5 chars only). Most focus on passwords; some specialize in malware or file integrity.

Question 3

Can hash lookup crack strong passwords?

Accepted Answer

No. Hash lookup only finds passwords already in breach databases or common dictionaries. Strong, unique passwords (16+ chars, random) rarely appear in databases. Lookup finds weak/reused passwords in minutes. Strong passwords require brute-force (years/centuries). Use this to verify password strength - if found, it is compromised. Change immediately.

Question 4

What is k-anonymity for hash lookup?

Accepted Answer

K-anonymity protects privacy during hash lookup. Instead of sending full hash (reveals exact password if database is malicious), send only first 5 characters. API returns all matching hashes. Client checks locally. Example: Hash 5BAA6... - send "5BAA6", receive ~500 matches, check offline. HIBP Pwned Passwords uses this. Prevents database from knowing your exact hash.

Question 5

How to use hash lookup for malware analysis?

Accepted Answer

Copy file hash (MD5/SHA-1/SHA-256) from malware sample. Search in VirusTotal, MalwareBazaar, or ThreatCrowd. Results show: antivirus detections, malware family, submission date, IOCs (IPs, domains, URLs), related samples. Hash lookup identifies known malware instantly. Unknown hash? Likely new variant - submit for sandbox analysis. Always use isolated VM for malware handling.

Question 6

What does "hash not found" mean?

Accepted Answer

Hash not found means the hash does not exist in the database searched. For passwords: good news - not in known breaches (but could still be weak). For files: unknown to that database (not necessarily safe - could be new malware). Search multiple databases. Hash not found ≠ secure. Use additional validation: password strength checks, antivirus scans.

Question 7

Should I use MD5 or SHA-256 for lookup?

Accepted Answer

Use SHA-256 for new systems (more secure, collision-resistant). MD5/SHA-1 acceptable only for legacy lookups in older databases. Many breach databases still use MD5 (faster, smaller). For file integrity or security, always use SHA-256+. For lookup: use hash type that matches your source (Windows logs = NTLM, Linux = SHA-512, web = bcrypt).

Question 8

Is hash lookup legal?

Accepted Answer

Yes, when used ethically: checking your own passwords, analyzing malware samples in research, incident response, threat intelligence, password policy validation. Illegal: cracking others passwords without authorization, accessing protected systems, distributing cracked passwords. Follow responsible disclosure. Comply with CFAA (US), Computer Misuse Act (UK). Research-only, no unauthorized access.

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