GPEN Password Attacks and Formats Practice Question
A penetration tester has obtained a hash from a Linux system: `$1$salt$hash`. The tester wants to crack it using John the Ripper. Which format should be specified, and what is the main weakness of this hash type?
⚠ Common exam trap
The trap here is assuming that any salted hash is slow to crack, but md5crypt's speed makes it relatively weak despite salting.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
md5crypt, and the main weakness is that it is fast to compute, making brute-force attacks easier.
The `$1$` prefix is the identifier for md5crypt. John the Ripper supports this format with the 'md5crypt' option. The primary weakness is that MD5 is a fast hash function, so despite salting and a fixed number of iterations, it can be cracked quickly using modern hardware. This makes it less secure than slower algorithms like bcrypt or SHA-512 crypt with high iteration counts.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
sha512crypt, and the main weakness is that the iteration count is too low by default.
Why it's wrong here
SHA-512 crypt uses the prefix `$6$`, not `$1$`. The default iteration count for SHA-512 crypt is 5000, which is not necessarily too low; it can be increased. This option confuses the hash type and its properties. Specifying sha512crypt would be incorrect for the given hash.
- ✗
descrypt, and the main weakness is that it only uses the first 8 characters of the password.
Why it's wrong here
DES crypt hashes are typically 13 characters long and do not have a `$1$` prefix. The `$1$` clearly indicates md5crypt. While descrypt does truncate passwords to 8 characters, that is not the case here. Using the descrypt format would not work for this hash. The tester must recognize the prefix to select the correct format.
- ✗
bcrypt, and the main weakness is that the salt is too short, allowing rainbow table attacks.
Why it's wrong here
Bcrypt uses the prefix `$2a$`, `$2b$`, or `$2y$`, not `$1$`. The salt in bcrypt is 128 bits, which is not short. This option misidentifies the hash and incorrectly states a weakness. Using the bcrypt format in John would fail to crack the md5crypt hash, wasting time.
- ✓
md5crypt, and the main weakness is that it is fast to compute, making brute-force attacks easier.
Why this is correct
The `$1$` prefix indicates md5crypt, which is based on MD5. John the Ripper uses the format 'md5crypt' for these hashes. The main weakness is that MD5 is fast, so even with salting and iterations, it can be cracked relatively quickly compared to slower algorithms like bcrypt. This makes it vulnerable to brute-force and dictionary attacks.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official GIAC exam blueprint
This GPEN practice question is part of Courseiva's free GIAC certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the GPEN exam.