SAIT - CPNT-225 - Day 3

Homework for Day 3, due next Monday:

Read the following:

• http://arstechnica.com/security/2012/08/passwords-under-assault/
• http://arstechnica.com/security/2012/12/25-gpu-cluster-cracks-every-standard-windows-password-in-6-hours/
• http://arstechnica.com/security/2013/05/how-crackers-make-minced-meat-out-of-your-passwords/

Password storage

1. What is a password hash?
   • A cryptographic hash function is a hash function which is considered practically impossible to invert, that is, to recreate the input data from its hash value alone.
2. What is an LM hash? What are LM’s main weaknesses?
   • is a compromised password hashing function that was the primary hash that Microsoft LAN Manager and Microsoft Windows versions prior to Windows NT used to store user passwords.
   • weaknesses: max 14 characters split into two halves, converted to uppercase, does not use salt.
3. How many character is an LM password split into before it is hashed?
   • 7
4. What is an NTLM hash?
   • successor to the LM hash.
5. What is a salt, and how is it used by NTLM?
   • Salt is a unique value that is used to ensure that if two users have the same password, the generated hash digest will be different.
   • It is typically stored with the users hash digest.
   • NTLM does not use salt.
6. What format is the hash you dumped in?
   • Lan Manager hash
7. What Windows local security policy setting prevents storage in LM?
   • Network security: Do not store LAN Manager hash value on next password change.
8. What must be done for this setting to take effect?
   • users much change their password.
9. What is an MD5 hash?
   • The MD5 message-digest algorithm is a widely used cryptographic hash function producing a 128-bit (16-byte) hash value, typically expressed in text format as a 32 digit hexadecimal number.
10. What advances due password storage mechanisms such as bcrypt or scrypt have over MD5?
    • they include salt and are designed to be more compute intensive to convert plaintext input into hashes.
    • Basically, it’s slow as hell.
11. What is a rainbow table, and how does it differ from a dictionary password guessing attack? From a brute force attack?
    • A rainbow table is a precomputed table for reversing cryptographic hash functions, usually for cracking password hashes.
    • the difference is that the rainbow tables are pre-computed hash digests, where a dictionary attach or brute force attach has to calculate the hashes on the fly and compare them to the target digest.

Go to FreeRainBowTables.com and look at the various rainbow tables.

1. What is a character set?
   • This is the letters that has been used to generate the tables.
   • Character set tells the rainbow table generator what kind of passwords there should be in the rainbow table.
2. What is the correlation between the coverage of a character set and the size of a rainbow table?
   • A higher chain length will require fewer chains (thus less diskspace) to reach 99.9% success rate, but the cracking time will increase with the square of the chainlength. So cracking time with a chainlength of 20000 will take 4 times longer than with chainlength 10000.
3. Why do you think NTLM tables are larger than LM?
   • the max number of characters in LM is 14 characters split in half. (two 7 character password before computing the digest.)
4. What format are these tables in? https://www.freerainbowtables.com/en/tables2/
   • The tables are in a custom format, RTI2, to save disk space (more than 50%!)
5. What is the approach used with Hashcat vs oclHashcat?
   • Hashcat: CPU based. runs on linux, osx, windows.
   • oclHashcat: - GPU-based, runs on linux and windows.
   • https://en.wikipedia.org/wiki/Hashcat
6. What is GPU cracking?
   • clustering several GPU’s together for the purpose of cracking passwords.
   • The advent of GPU computing over the past decade has contributed to huge boosts in offline password cracking.
7. Why is GPU cracking faster than CPU?
   • GPUs are designed with one goal in mind: process graphics really fast. Since this is the only concern they have, there have been some specialized optimizations in place that allow for certain calculations to go a LOT faster than they would in a traditional processor.

Network Authentication Describe the following:

1. NTLMv2
   • is a challenge-response authentication protocol. It is intended as a cryptographically strengthened replacement for NTLMv1
2. Kerberos
   • a client–server model and it provides mutual authentication—both the user and the server verify each other’s identity. Kerberos protocol messages are protected against eavesdropping and replay attacks.
3. Basic Authentication
   • To receive authorization, the client sends the userid and password, separated by a single colon (“:”) character, within a base64 encoded string in the credentials.

Bonus reading (not required):

• Mudge’s original ezine rant on LM- https://dl.packetstormsecurity.net/Crackers/NT/l0phtcrack/l0phtcrack.rant.nt.passwd.txt