Swap out hash function for obfuscated IDs

secretlounge_ng/database.py

@@ -24,6 +24,8 @@ def defaults(self):
 	"hideKarma", "debugEnabled", "tripcode"
 )
 
+ID_ALPHA = "0123456789abcdefghijklmnopqrstuv"
+
 class User():
 	__slots__ = USER_PROPS
 	id: int
@@ -66,10 +68,9 @@ def isBlacklisted(self):
 		return self.rank < 0
 	def getObfuscatedId(self):
 		salt = date.today().toordinal()
-		if salt & 0xff == 0: salt >>= 8 # zero bits are bad for hashing
-		value = (self.id * salt) & 0xffffff
-		alpha = "0123456789abcdefghijklmnopqrstuv"
-		return ''.join(alpha[n%32] for n in (value, value>>5, value>>10, value>>15))
+		value = fnv32a([self.id, salt], [])
+		# stringify 20 bits
+		return ''.join(ID_ALPHA[n%32] for n in (value, value>>5, value>>10, value>>15))
 	def getObfuscatedKarma(self):
 		for cutoff in (100, 50, 10):
 			if abs(self.karma) >= cutoff:

secretlounge_ng/globals.py

@@ -24,6 +24,21 @@ def format_timedelta(d):
 			return "%d%c" % (d // cmp, char)
 	return "%ds" % d.total_seconds()
 
+# 32-bit FNV-1a
+def fnv32a(int_parts, byte_parts) -> int:
+	h = 0x811c9dc5
+	p = 0x01000193
+	for i in int_parts:
+		i = abs(i)
+		# trivial little endian encoding
+		while i != 0:
+			h = ((h ^ (i & 0xff)) * p) & 0xffffffff
+			i >>= 8
+	for bs in byte_parts:
+		for b in bs:
+			h = ((h ^ b) * p) & 0xffffffff
+	return h
+
 ## for debugging ##
 def dump(obj, name=None, r=False):
 	name = (name + ".") if name else ""