From 580f2c4f67b218fa6df2e5021ceb21493cfd0de4 Mon Sep 17 00:00:00 2001
From: PlexSheep <software@cscherr.de>
Date: Thu, 1 Jun 2023 17:50:40 +0200
Subject: [PATCH] oaep inner works

---
 src-py/plexcryptool/scripts/oaep_rsa.py | 83 +++++++++++++++++++------
 1 file changed, 65 insertions(+), 18 deletions(-)

diff --git a/src-py/plexcryptool/scripts/oaep_rsa.py b/src-py/plexcryptool/scripts/oaep_rsa.py
index 8d2d7c5..4964a67 100755
--- a/src-py/plexcryptool/scripts/oaep_rsa.py
+++ b/src-py/plexcryptool/scripts/oaep_rsa.py
@@ -8,6 +8,7 @@ Perform RSA-OAEP
 """
 
 import hashlib
+import random
 from math import floor
 
 # the given key in the assignment
@@ -39,21 +40,39 @@ def mgf1(seed: bytearray, length: int, hash_func=hashlib.sha256) -> bytearray:
     # 4.Output the leading l octets of T as the octet string mask.
     return bytearray(T[:length])
 
-def byte_xor(ba1: bytearray, ba2: bytearray):
-    a = int(ba1.hex(), 16)
-    b = int(ba2.hex(), 16)
-    c = a^b
-    if c.bit_length() / 8 == floor(c.bit_length() / 8):
-        clen = floor(c.bit_length() / 8)
-    else:
-        clen = floor(c.bit_length() / 8) + 1
-    return bytearray(c.to_bytes(clen, 'big'))
+def byte_xor(ba0: bytearray, ba1: bytearray):
+    """
+    helper function for bytewise xor
+    """
+    ba2: bytearray = bytearray(0)
+    for (b0, b1) in zip(ba0, ba1):
+        ba2.append((b0 ^ b1))
+    #print("xored:\n%s" % ba2.hex())
+    return ba2
 
+def calclen(n: int) -> int:
+    """
+    helper function to calculate the length in bytes
+    """
+    len = n.bit_length() / 8
+    if len > floor(len):
+        return 1 + floor(len)
+    else: 
+        return floor(len)
 
-def rsa_oaep_inner(seed: bytearray, datablock: bytearray) -> tuple[bytearray, bytearray, bytearray]:
-    mgf_seed = mgf1(seed, len(seed))
-    masked_db = byte_xor(mgf_seed, datablock)
-    print(masked_db.hex())
+def rsa_oaep_inner(seed: bytearray, block: bytearray) -> tuple[bytearray, bytearray]:
+    """
+    inner function of rsa-oaep
+    """
+    mgf_seed = mgf1(seed, len(block))
+    print("mgf1(seed):\n%s" % mgf_seed.hex())
+    masked_db = byte_xor(mgf_seed, block)
+    print("mgf1(seed) ^ block:\n%s" % masked_db.hex())
+    mask_seed = mgf1(masked_db, len(seed))
+    print("mgf1(mgf1(seed) ^ block):\n%s" % mask_seed.hex())
+    masked_seed = byte_xor(seed, mask_seed)
+    print("mgf1(mgf1(seed) ^ block) ^ seed:\n%s" % masked_seed.hex())
+    return (masked_seed, masked_db)
 
 def test_rsa_oaep_inner():
     seed: bytearray = bytearray.fromhex("aa1122fe0815beef")
@@ -64,8 +83,8 @@ def test_rsa_oaep_inner():
     00000000000000000000000000000000000001466f6f626172203132
     33343536373839
     """)
-    print("seed\t%s" % seed.hex())
-    print("db\t%s" % db.hex())
+    print("seed:\n%s" % seed.hex())
+    print("db:\n%s" % db.hex())
 
     result = rsa_oaep_inner(seed, db)
 
@@ -85,8 +104,36 @@ def test_rsa_oaep_inner():
     """)
     GIVEN_MASK_FOR_SEED = bytearray.fromhex("713162084a4e0e6d ")
     GIVEN_MASKED_SEED = bytearray.fromhex("db2040f6425bb082")
-    assert result[0] == GIVEN_MASKED_SEED, "is %s" % result[0].hex()
-    assert result[1] == GIVEN_MASKED_DB, "is %s" % result[1].hex()
+    assert result[0] == GIVEN_MASKED_SEED, "is\n%s\ninstead of\n%s" % (result[0].hex(), GIVEN_MASKED_SEED.hex())
+    assert result[1] == GIVEN_MASKED_DB, "is\n%s\ninstead of\n%s" % (result[1].hex(), GIVEN_MASKED_DB.hex())
+
+def rsa_oaep(ha: bytearray, m: bytearray):
+    # generate a seed
+    seed = random.randint(0, 2**64 - 1)
+    seed = bytearray(seed.to_bytes(calclen(seed), 'big'))
+    # build the message
+    block: bytearray = bytearray(0)
+    assert len(block) == 0
+    curlen = 0
+    curlen += len(ha)
+    curlen += len(m)
+    block += ha
+    block += bytearray(calclen(GIVEN_PUB_KEY[0]) - curlen)
+    block += m
+
+    assert len(block) == calclen(GIVEN_PUB_KEY[0]), "curlen:\n%s\nmodlen:\n%s" % (curlen, calclen(GIVEN_PUB_KEY[0]))
+    result = rsa_oaep_inner(seed, block)
+    print()
+    print(result[0].hex())
+    print(result[1].hex())
+    print()
+    return bytearray(1) + result[0] + result[1]
+
+def main():
+    ha = bytearray(0)
+    m = bytearray.fromhex("466f6f62617220313233343536373839")
+    r = rsa_oaep(ha, m)
+    print("final:\n%s" % r.hex())
 
 if __name__ == "__main__":
-    test_rsa_oaep_inner()
+    main()