1 files changed, 66 insertions, 0 deletions
diff --git a/app/util.py b/app/util.py
new file mode 100644
index 0000000..69b3ea7
--- /dev/null
+++ b/app/util.py
@@ -0,0 +1,66 @@
+from base64 import b32encode, b32decode
+import logging
+from hashlib import blake2b  # because it is fast as fuck
+
+log = logging.getLogger('blure')
+
+
+class URLCoder:
+    '''
+    URLCoder shuffles sequential ids into non-sequential strings,
+    that can be used as urls
+    '''
+    _pad = 1
+    _bs = 2
+    _bound = 2 ** (8 * _bs * 2)
+    _endian = 'big'
+
+    @classmethod
+    def _humanify(self, data: bytes):
+        b32 = b32encode(data).decode('ascii')
+        if self._pad > 0:
+            return b32[:-self._pad]
+        else:
+            return b32
+
+    @classmethod
+    def _dehumanify(self, data: str):
+        binary = b32decode(data + '=' * self._pad)
+        assert len(binary) == self._bs * 2
+        return binary
+
+    def __init__(self, secret: bytes):
+        assert len(secret) % (self._bs) == 0
+
+        self.keys = [
+            secret[key_start:key_start + self._bs]
+            for key_start in range(0, len(secret), self._bs)
+        ]
+        self.reverse_keys = self.keys[::-1]
+
+    def to_url(self, id: int) -> str:
+        assert 0 <= id and id <= self._bound
+        as_bytes = int.to_bytes(id, self._bs * 2, self._endian)
+        encoded = self._blake_enc(as_bytes, self.keys)
+        return self._humanify(encoded)
+
+    def to_id(self, url: str) -> int:
+        binary = self._dehumanify(url.upper())
+        as_bytes = self._blake_enc(binary, self.reverse_keys)
+        return int.from_bytes(as_bytes, self._endian)
+
+    def _blake_enc(self, data: bytes, keys: bytes):
+        bs = self._bs
+
+        def xor(bytes1, bytes2):
+            return bytes([b1 ^ b2 for b1, b2 in zip(bytes1, bytes2)])
+
+        def blake_round(data, key):
+            return blake2b(data, digest_size=bs, key=key).digest()
+
+        left = data[:bs]
+        right = data[bs:]
+        for key in keys:
+            left, right = right, xor(left, blake_round(right, key))
+
+        return right + left