DavidBuchanan314 · September 14, 2025 16:21 · Mar 27, 2024 · Mar 27, 2024 · Mar 27, 2024 · Mar 27, 2024
diff --git a/31_round_sha256_poc.py b/31_round_sha256_poc.py
@@ -4,6 +4,8 @@
 Not my research, just a PoC script I put together with numbers plugged in from the slide at
 https://twitter.com/jedisct1/status/1772647350554464448 from FSE2024
 
+SHA256 impl follows FIPS 180-4
+https://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.180-4.pdf
 """
 
 
@@ -69,7 +71,6 @@ def word_iterator(m):
 
 
 # Section 5.3.3
-# See derivations/sha.py for the derivation of these constants.
 initial_H = [
 	0x6a09e667,
 	0xbb67ae85,

diff --git a/31_round_sha256_poc.py b/31_round_sha256_poc.py
@@ -4,7 +4,6 @@
 Not my research, just a PoC script I put together with numbers plugged in from the slide at
 https://twitter.com/jedisct1/status/1772647350554464448 from FSE2024
 
-Edit: relevant paper: https://eprint.iacr.org/2024/349
 """
 
 

diff --git a/31_round_sha256_poc.py b/31_round_sha256_poc.py
@@ -3,6 +3,8 @@
 
 Not my research, just a PoC script I put together with numbers plugged in from the slide at
 https://twitter.com/jedisct1/status/1772647350554464448 from FSE2024
+
+Edit: relevant paper: https://eprint.iacr.org/2024/349
 """
 
 

diff --git a/31_round_sha256_poc.py b/31_round_sha256_poc.py
@@ -148,4 +148,4 @@ def sha256_31(blocks):
 	h2 = sha256_31([m0, m1b])
 	print(h2.hex())
 
-	assert(h1 == h1)  # they're the same!!!
+	assert(h1 == h2)  # they're the same!!!
diff --git a/31_round_sha256_poc.py b/31_round_sha256_poc.py
@@ -1,7 +1,7 @@
 """
 31-round sha256 collision.
 
-Not my research, just a PoC script I put together based on the slide at
+Not my research, just a PoC script I put together with numbers plugged in from the slide at
 https://twitter.com/jedisct1/status/1772647350554464448 from FSE2024
 """
 

diff --git a/31_round_sha256_poc.py b/31_round_sha256_poc.py
@@ -0,0 +1,151 @@
+"""
+31-round sha256 collision.
+
+Not my research, just a PoC script I put together based on the slide at
+https://twitter.com/jedisct1/status/1772647350554464448 from FSE2024
+"""
+
+
+# Section 2.2.2
+def rotr(x, n):
+	return ((x >> n) | (x << (32 - n))) & 0xFFFFFFFF
+
+
+# Section 2.2.2
+def shr(x, n):
+	return x >> n
+
+
+# Section 4.1.2 (4.2)
+def Ch(x, y, z):
+	return (x & y) ^ (~x & z)
+
+
+# Section 4.1.2 (4.3)
+def Maj(x, y, z):
+	return (x & y) ^ (x & z) ^ (y & z)
+
+
+# Section 4.1.2 (4.4)
+def S0(x):
+	return rotr(x, 2) ^ rotr(x, 13) ^ rotr(x, 22)
+
+
+# Section 4.1.2 (4.5)
+def S1(x):
+	return rotr(x, 6) ^ rotr(x, 11) ^ rotr(x, 25)
+
+
+# Section 4.1.2 (4.6)
+def s0(x):
+	return rotr(x, 7) ^ rotr(x, 18) ^ shr(x, 3)
+
+
+# Section 4.1.2 (4.7)
+def s1(x):
+	return rotr(x, 17) ^ rotr(x, 19) ^ shr(x, 10)
+
+
+"""
+Section 4.2.2 - SHA-256 Constants
+"""
+K = [
+	0x428a2f98, 0x71374491, 0xb5c0fbcf, 0xe9b5dba5, 0x3956c25b, 0x59f111f1, 0x923f82a4, 0xab1c5ed5,
+	0xd807aa98, 0x12835b01, 0x243185be, 0x550c7dc3, 0x72be5d74, 0x80deb1fe, 0x9bdc06a7, 0xc19bf174,
+	0xe49b69c1, 0xefbe4786, 0x0fc19dc6, 0x240ca1cc, 0x2de92c6f, 0x4a7484aa, 0x5cb0a9dc, 0x76f988da,
+	0x983e5152, 0xa831c66d, 0xb00327c8, 0xbf597fc7, 0xc6e00bf3, 0xd5a79147, 0x06ca6351, 0x14292967,
+	0x27b70a85, 0x2e1b2138, 0x4d2c6dfc, 0x53380d13, 0x650a7354, 0x766a0abb, 0x81c2c92e, 0x92722c85,
+	0xa2bfe8a1, 0xa81a664b, 0xc24b8b70, 0xc76c51a3, 0xd192e819, 0xd6990624, 0xf40e3585, 0x106aa070,
+	0x19a4c116, 0x1e376c08, 0x2748774c, 0x34b0bcb5, 0x391c0cb3, 0x4ed8aa4a, 0x5b9cca4f, 0x682e6ff3,
+	0x748f82ee, 0x78a5636f, 0x84c87814, 0x8cc70208, 0x90befffa, 0xa4506ceb, 0xbef9a3f7, 0xc67178f2,
+]
+
+
+# Section 5.2.1
+def word_iterator(m):
+	for i in range(0, len(m), 32//8):
+		yield int.from_bytes(m[i:i+32//8], "big")
+
+
+# Section 5.3.3
+# See derivations/sha.py for the derivation of these constants.
+initial_H = [
+	0x6a09e667,
+	0xbb67ae85,
+	0x3c6ef372,
+	0xa54ff53a,
+	0x510e527f,
+	0x9b05688c,
+	0x1f83d9ab,
+	0x5be0cd19,
+]
+
+
+# Section 6.2
+def sha256_31(blocks):
+	# 6.2.1, 1) Initialize H
+	H = initial_H.copy()
+
+	NUM_ROUNDS = 31 # XXX: normally 64!
+
+	# 6.2.2 - SHA-256 Hash Computation
+	for block in blocks:
+
+		# 1. Prepare the message schedule
+		W = list(word_iterator(block))
+		for t in range(16, NUM_ROUNDS):
+			W.append((s1(W[t-2]) + W[t-7] + s0(W[t-15]) + W[t-16]) & 0xFFFFFFFF)
+
+		# 2. Initialize the eight working variables
+		a, b, c, d, e, f, g, h = H
+
+		# 3.
+		for t in range(NUM_ROUNDS):
+			T1 = h + S1(e) + Ch(e, f, g) + K[t] + W[t]
+			T2 = S0(a) + Maj(a, b, c)
+			h = g
+			g = f
+			f = e
+			e = (d + T1) & 0xFFFFFFFF
+			d = c
+			c = b
+			b = a
+			a = (T1 + T2) & 0xFFFFFFFF
+
+		# 4. Calculate the next Hash value
+		for i, x in enumerate((a, b, c, d, e, f, g, h)):
+			H[i] = (H[i] + x) & 0xFFFFFFFF
+
+	# convert the result to bytes
+	M = b""
+	for word in H:
+		M += word.to_bytes(32//8, "big")
+	return M
+
+
+
+if __name__ == "__main__":
+	m0 = bytes.fromhex("""
+		c32aef52 512294ba 9db5ed8c 8c8c88ed b2de2765 63a2d14e ec7619cc 93b21182
+		e5050f50 f0839b60 7b1ee176 aaa06d68 c462343c 67898962 9558f495 04281f2c
+	""")
+
+	m1a = bytes.fromhex("""
+		5d0f5ae6 05e98311 8fa3c73a 9af8c49d a2bf31f7 de547b67 5baecee3 da0d8c94
+		e4c19564 f682d45c f7c57698 f871f9b5 f14469b7 fc28eb0c 2d76db75 043fe071
+	""")
+
+	m1b = bytes.fromhex("""
+		5d0f5ae6 05e98311 8fa3c73a 9af8c49d a2bf31f7 de548b61 5b8e46f2 8a1dd69a
+		bcc08464 f6825458 f7c57698 f871f9b5 f14469b7 fc28eb0c 2d76db75 043fe071
+	""")
+
+	assert(m1a != m1b)  # they're different
+
+	h1 = sha256_31([m0, m1a])
+	print(h1.hex())
+
+	h2 = sha256_31([m0, m1b])
+	print(h2.hex())
+
+	assert(h1 == h1)  # they're the same!!!