complete set02/09

set02/09_code.py

@@ -0,0 +1,19 @@
+#!/usr/bin/env python3
+
+from common_set02 import pkcs7
+
+def main():
+    bts_unpadded = b'YELLOW SUBMARINE'
+
+    bts_padded = pkcs7(bts_unpadded, 20)
+
+    assert(bts_padded == b'YELLOW SUBMARINE\x04\x04\x04\x04')
+
+    s = (
+        'bts_unpadded: \'{}\'\n'
+        'bts_padded:   \'{}\'\n'
+    )
+    print(s.format(bts_unpadded, bts_padded), end='')
+
+if __name__ == "__main__":
+    main()

set02/common_set02/__init__.py

@@ -0,0 +1 @@
+from .utils import pkcs7

set02/common_set02/utils.py

@@ -0,0 +1,17 @@
+import math
+
+def pkcs7(bts, blk_size: int):
+    """
+    bts: bytes to right pad
+    blk_size: int < 256
+
+    Right-pad bts until blk_size divides len(bts).
+    The byte value to pad with is the number bytes padded.
+
+    returns: the padded bts
+    """
+    if not blk_size < 256:
+        raise ValueError('need blk_size < 256')
+
+    pad = abs(len(bts) - math.ceil(len(bts) / blk_size) * blk_size)
+    return bytes(pad if not i < len(bts) else bts[i] for i in range(len(bts)+pad))