hash-attack-techniques

Name: hash-attack-techniques
Author: Prohao42

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How to install hash-attack-techniques?

prohao42/aimy-skill/hash-attack-techniques

$npx -y skills add Prohao42/aimy-skill --skill hash-attack-techniques

Installs into the current project.

Summary

Hash attack playbook. Use when exploiting length extension, MD5/SHA1 collisions, HMAC timing leaks, birthday attacks, or hash-based proof of work in CTF and authorized testing scenarios.

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SKILL.md

1	# SKILL: Hash Attack Techniques — Expert Cryptanalysis Playbook
2
3	> AI LOAD INSTRUCTION: Expert hash attack techniques for CTF and security assessments. Covers length extension attacks, MD5/SHA1 collision generation, meet-in-the-middle hash attacks, HMAC timing side channels, birthday attacks, and proof-of-work solving. Base models often incorrectly apply length extension to HMAC or SHA-3, or fail to distinguish between identical-prefix and chosen-prefix collisions.
4
5	## 0. RELATED ROUTING
6
7	- [rsa-attack-techniques](../rsa-attack-techniques/SKILL.md) when hash weaknesses affect RSA signature schemes
8	- [symmetric-cipher-attacks](../symmetric-cipher-attacks/SKILL.md) when hash is used in key derivation
9	- [classical-cipher-analysis](../classical-cipher-analysis/SKILL.md) when analyzing hash-like constructions in classical ciphers
10
11	### Quick attack selection
12
13	\| Scenario \| Attack \| Tool \|
14	\|---\|---\|---\|
15	\| `H(secret \\|\\| msg)` known, extend message \| Length extension \| HashPump, hash_extender \|
16	\| Need two files with same MD5 \| Identical-prefix collision \| fastcoll \|
17	\| Need specific MD5 prefix match \| Chosen-prefix collision \| hashclash \|
18	\| Byte-by-byte HMAC comparison \| Timing attack \| Custom script \|
19	\| Find any collision \| Birthday attack \| O(2^(n/2)) \|
20	\| Proof of work: find hash with leading zeros \| Brute force \| hashcat, Python \|
21
22	---
23
24	## 1. LENGTH EXTENSION ATTACK
25
26	### 1.1 Vulnerable vs Non-Vulnerable
27
28	\| Hash \| Vulnerable \| Why \|
29	\|---\|---\|---\|
30	\| MD5 \| Yes \| Merkle-Damgard construction \|
31	\| SHA-1 \| Yes \| Merkle-Damgard construction \|
32	\| SHA-256 \| Yes \| Merkle-Damgard construction \|
33	\| SHA-512 \| Yes \| Merkle-Damgard construction \|
34	\| SHA-3 / Keccak \| No \| Sponge construction \|
35	\| HMAC-* \| No \| Double hashing prevents extension \|
36	\| SHA-256 truncated \| No (if truncated) \| Missing internal state bits \|
37	\| BLAKE2 \| No \| Different construction \|
38
39	### 1.2 Attack Mechanism
40
41	```
42	Given: MAC = H(secret \|\| original_message)
43	Known: original_message, len(secret), MAC value
44	Compute: H(secret \|\| original_message \|\| padding \|\| extension)
45	WITHOUT knowing the secret!
46
47	How: The MAC value IS the internal hash state after processing
48	(secret \|\| original_message \|\| padding).
49	Initialize hash with this state, continue hashing extension.
50	```
51
52	### 1.3 Padding Calculation (MD5/SHA)
53
54	```python
55	def md5_padding(message_len_bytes):
56	"""Calculate MD5/SHA padding for given message length."""
57	bit_len = message_len_bytes * 8
58
59	# Pad with 0x80 + zeros until length ≡ 56 (mod 64)
60	padding = b'\x80'
61	padding += b'\x00' * ((55 - message_len_bytes) % 64)
62
63	# Append original length as 64-bit little-endian (MD5)
64	# or big-endian (SHA)
65	padding += bit_len.to_bytes(8, 'little') # MD5
66	# padding += bit_len.to_bytes(8, 'big') # SHA
67
68	return padding
69	```
70
71	### 1.4 Tool Usage
72
73	```bash
74	# HashPump
75	hashpump -s "known_mac_hex" \
76	-d "original_data" \
77	-k 16 \ # secret length
78	-a "extension_data"
79
80	# Output: new_mac, new_data (original + padding + extension)
81
82	# hash_extender
83	hash_extender --data "original" \
84	--secret 16 \
85	--append "extension" \
86	--signature "known_mac_hex" \
87	--format md5
88	```
89
90	### 1.5 Python Implementation
91
92	```python
93	import struct
94
95	def md5_extend(original_mac, original_data_len, secret_len, extension):
96	"""
97	Perform MD5 length extension attack.
98	original_mac: hex string of H(secret \|\| original_data)
99	"""
100	# Parse MAC into MD5 internal state (4 × 32-bit words, little-endian)
101	h = struct.unpack('<4I', bytes.fromhex(original_mac))
102
103	# Calculate total length after padding
104	total_original = secret_len + original_data_len
105	padding = md5_padding(total_original)
106	forged_len = total_original + len(padding) + len(extension)
107
108	# Continue MD5 from saved state with extension
109	# (requires MD5 implementation that accepts initial state)
110	from hashlib import md5
111	# Most stdlib md5 doesn't expose state setting
112	# Use: hlextend library or custom MD5
113
114	import hlextend
115	sha = hlextend.new('md5')
116	new_hash = sha.extend(extension, original_data, secret_len,
117	original_mac)
118	new_data = sha.payload # includes original + padding + extension
119
120	return new_hash, new_data
121	```
122
123	---
124
125	## 2. MD5 COLLISION ATTACKS
126
127	### 2.1 Identical-Prefix Collision (fastcoll)
128
129	Two messages with same prefix but different content, producing identical MD5.
130
131	```bash
132	# Generate collision pair
133	fastcoll -p prefix_file -o collision1.bin collision2.bin
134
135	# Result: MD5(collision1.bin) == MD5(collision2.bin)
136	# Files differ in exactly 128 bytes (two MD5 blocks)
137	```
138
139	### 2.2 Chosen-Prefix Collision (hashclash)
140
141	Two messages with different chosen pref

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hash-attack-techniques

91stars8forks

View on GitHub

How to install hash-attack-techniques?

prohao42/aimy-skill/hash-attack-techniques

$npx -y skills add Prohao42/aimy-skill --skill hash-attack-techniques

Installs into the current project.

Summary

Hash attack playbook. Use when exploiting length extension, MD5/SHA1 collisions, HMAC timing leaks, birthday attacks, or hash-based proof of work in CTF and authorized testing scenarios.

Files · 1

View on GitHub

SKILL.md

1	# SKILL: Hash Attack Techniques — Expert Cryptanalysis Playbook
2
3	> AI LOAD INSTRUCTION: Expert hash attack techniques for CTF and security assessments. Covers length extension attacks, MD5/SHA1 collision generation, meet-in-the-middle hash attacks, HMAC timing side channels, birthday attacks, and proof-of-work solving. Base models often incorrectly apply length extension to HMAC or SHA-3, or fail to distinguish between identical-prefix and chosen-prefix collisions.
4
5	## 0. RELATED ROUTING
6
7	- [rsa-attack-techniques](../rsa-attack-techniques/SKILL.md) when hash weaknesses affect RSA signature schemes
8	- [symmetric-cipher-attacks](../symmetric-cipher-attacks/SKILL.md) when hash is used in key derivation
9	- [classical-cipher-analysis](../classical-cipher-analysis/SKILL.md) when analyzing hash-like constructions in classical ciphers
10
11	### Quick attack selection
12
13	\| Scenario \| Attack \| Tool \|
14	\|---\|---\|---\|
15	\| `H(secret \\|\\| msg)` known, extend message \| Length extension \| HashPump, hash_extender \|
16	\| Need two files with same MD5 \| Identical-prefix collision \| fastcoll \|
17	\| Need specific MD5 prefix match \| Chosen-prefix collision \| hashclash \|
18	\| Byte-by-byte HMAC comparison \| Timing attack \| Custom script \|
19	\| Find any collision \| Birthday attack \| O(2^(n/2)) \|
20	\| Proof of work: find hash with leading zeros \| Brute force \| hashcat, Python \|
21
22	---
23
24	## 1. LENGTH EXTENSION ATTACK
25
26	### 1.1 Vulnerable vs Non-Vulnerable
27
28	\| Hash \| Vulnerable \| Why \|
29	\|---\|---\|---\|
30	\| MD5 \| Yes \| Merkle-Damgard construction \|
31	\| SHA-1 \| Yes \| Merkle-Damgard construction \|
32	\| SHA-256 \| Yes \| Merkle-Damgard construction \|
33	\| SHA-512 \| Yes \| Merkle-Damgard construction \|
34	\| SHA-3 / Keccak \| No \| Sponge construction \|
35	\| HMAC-* \| No \| Double hashing prevents extension \|
36	\| SHA-256 truncated \| No (if truncated) \| Missing internal state bits \|
37	\| BLAKE2 \| No \| Different construction \|
38
39	### 1.2 Attack Mechanism
40
41	```
42	Given: MAC = H(secret \|\| original_message)
43	Known: original_message, len(secret), MAC value
44	Compute: H(secret \|\| original_message \|\| padding \|\| extension)
45	WITHOUT knowing the secret!
46
47	How: The MAC value IS the internal hash state after processing
48	(secret \|\| original_message \|\| padding).
49	Initialize hash with this state, continue hashing extension.
50	```
51
52	### 1.3 Padding Calculation (MD5/SHA)
53
54	```python
55	def md5_padding(message_len_bytes):
56	"""Calculate MD5/SHA padding for given message length."""
57	bit_len = message_len_bytes * 8
58
59	# Pad with 0x80 + zeros until length ≡ 56 (mod 64)
60	padding = b'\x80'
61	padding += b'\x00' * ((55 - message_len_bytes) % 64)
62
63	# Append original length as 64-bit little-endian (MD5)
64	# or big-endian (SHA)
65	padding += bit_len.to_bytes(8, 'little') # MD5
66	# padding += bit_len.to_bytes(8, 'big') # SHA
67
68	return padding
69	```
70
71	### 1.4 Tool Usage
72
73	```bash
74	# HashPump
75	hashpump -s "known_mac_hex" \
76	-d "original_data" \
77	-k 16 \ # secret length
78	-a "extension_data"
79
80	# Output: new_mac, new_data (original + padding + extension)
81
82	# hash_extender
83	hash_extender --data "original" \
84	--secret 16 \
85	--append "extension" \
86	--signature "known_mac_hex" \
87	--format md5
88	```
89
90	### 1.5 Python Implementation
91
92	```python
93	import struct
94
95	def md5_extend(original_mac, original_data_len, secret_len, extension):
96	"""
97	Perform MD5 length extension attack.
98	original_mac: hex string of H(secret \|\| original_data)
99	"""
100	# Parse MAC into MD5 internal state (4 × 32-bit words, little-endian)
101	h = struct.unpack('<4I', bytes.fromhex(original_mac))
102
103	# Calculate total length after padding
104	total_original = secret_len + original_data_len
105	padding = md5_padding(total_original)
106	forged_len = total_original + len(padding) + len(extension)
107
108	# Continue MD5 from saved state with extension
109	# (requires MD5 implementation that accepts initial state)
110	from hashlib import md5
111	# Most stdlib md5 doesn't expose state setting
112	# Use: hlextend library or custom MD5
113
114	import hlextend
115	sha = hlextend.new('md5')
116	new_hash = sha.extend(extension, original_data, secret_len,
117	original_mac)
118	new_data = sha.payload # includes original + padding + extension
119
120	return new_hash, new_data
121	```
122
123	---
124
125	## 2. MD5 COLLISION ATTACKS
126
127	### 2.1 Identical-Prefix Collision (fastcoll)
128
129	Two messages with same prefix but different content, producing identical MD5.
130
131	```bash
132	# Generate collision pair
133	fastcoll -p prefix_file -o collision1.bin collision2.bin
134
135	# Result: MD5(collision1.bin) == MD5(collision2.bin)
136	# Files differ in exactly 128 bytes (two MD5 blocks)
137	```
138
139	### 2.2 Chosen-Prefix Collision (hashclash)
140
141	Two messages with different chosen pref

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