xuyao - SECCON 2023
配布されたバイナリを解析すると、以下のようなアルゴリズムで入力値を暗号化していることがわかった。
code:python
cat =0xec656287, 0xd9a22031, 0x1c7bca8, 0xabe7033b, 0x313fe5dc, 0x940ffad0, 0x176edeb8, 0x7c61b20e, 0x9ead452f, 0x80e2c15b, 0xba500d7b, 0xa2c0449f, 0xbc0e774f, 0x3e393763, 0x43d46b3f, 0x2adef404, 0xca884b87, 0x3c953c45, 0x7cdbde63, 0x6e995945, 0xb6cf3655, 0x8d60396a, 0x9a496b38, 0x9d87d81b, 0x36fedbc9, 0x79882953, 0x10611e15, 0x30ab3e, 0x12503487, 0x187e21ff, 0x6d85127e, 0xdf42c76c sbox = 0x63, 0x7c, 0x77, 0x7b, 0xf2, 0x6b, 0x6f, 0xc5, 0x30, 0x01, 0x67, 0x2b, 0xfe, 0xd7, 0xab, 0x76, 0xca, 0x82, 0xc9, 0x7d, 0xfa, 0x59, 0x47, 0xf0, 0xad, 0xd4, 0xa2, 0xaf, 0x9c, 0xa4, 0x72, 0xc0, 0xb7, 0xfd, 0x93, 0x26, 0x36, 0x3f, 0xf7, 0xcc, 0x34, 0xa5, 0xe5, 0xf1, 0x71, 0xd8, 0x31, 0x15, 0x04, 0xc7, 0x23, 0xc3, 0x18, 0x96, 0x05, 0x9a, 0x07, 0x12, 0x80, 0xe2, 0xeb, 0x27, 0xb2, 0x75, 0x09, 0x83, 0x2c, 0x1a, 0x1b, 0x6e, 0x5a, 0xa0, 0x52, 0x3b, 0xd6, 0xb3, 0x29, 0xe3, 0x2f, 0x84, 0x53, 0xd1, 0x00, 0xed, 0x20, 0xfc, 0xb1, 0x5b, 0x6a, 0xcb, 0xbe, 0x39, 0x4a, 0x4c, 0x58, 0xcf, 0xd0, 0xef, 0xaa, 0xfb, 0x43, 0x4d, 0x33, 0x85, 0x45, 0xf9, 0x02, 0x7f, 0x50, 0x3c, 0x9f, 0xa8, 0x51, 0xa3, 0x40, 0x8f, 0x92, 0x9d, 0x38, 0xf5, 0xbc, 0xb6, 0xda, 0x21, 0x10, 0xff, 0xf3, 0xd2, 0xcd, 0x0c, 0x13, 0xec, 0x5f, 0x97, 0x44, 0x17, 0xc4, 0xa7, 0x7e, 0x3d, 0x64, 0x5d, 0x19, 0x73, 0x60, 0x81, 0x4f, 0xdc, 0x22, 0x2a, 0x90, 0x88, 0x46, 0xee, 0xb8, 0x14, 0xde, 0x5e, 0x0b, 0xdb, 0xe0, 0x32, 0x3a, 0x0a, 0x49, 0x06, 0x24, 0x5c, 0xc2, 0xd3, 0xac, 0x62, 0x91, 0x95, 0xe4, 0x79, 0xe7, 0xc8, 0x37, 0x6d, 0x8d, 0xd5, 0x4e, 0xa9, 0x6c, 0x56, 0xf4, 0xea, 0x65, 0x7a, 0xae, 0x08, 0xba, 0x78, 0x25, 0x2e, 0x1c, 0xa6, 0xb4, 0xc6, 0xe8, 0xdd, 0x74, 0x1f, 0x4b, 0xbd, 0x8b, 0x8a, 0x70, 0x3e, 0xb5, 0x66, 0x48, 0x03, 0xf6, 0x0e, 0x61, 0x35, 0x57, 0xb9, 0x86, 0xc1, 0x1d, 0x9e, 0xe1, 0xf8, 0x98, 0x11, 0x69, 0xd9, 0x8e, 0x94, 0x9b, 0x1e, 0x87, 0xe9, 0xce, 0x55, 0x28, 0xdf, 0x8c, 0xa1, 0x89, 0x0d, 0xbf, 0xe6, 0x42, 0x68, 0x41, 0x99, 0x2d, 0x0f, 0xb0, 0x54, 0xbb, 0x16 enc = 0xfe, 0x60, 0xa8, 0xc0, 0x3b, 0xfe, 0xbc, 0x66, 0xfc, 0x9a, 0x9b, 0x31, 0x9a, 0xd8, 0x03, 0xbb, 0xa9, 0xe1, 0x56, 0xfc, 0xfc, 0x11, 0x9f, 0x89, 0x5f, 0x4d, 0x9f, 0xe0, 0x9f, 0xae, 0x2a, 0xcf, 0x5e, 0x73, 0xcb, 0xec, 0x3f, 0xff, 0xb9, 0xd1, 0x99, 0x44, 0x1b, 0x9a, 0x79, 0x79, 0xec, 0xd1, 0xb4, 0xfd, 0xea, 0x2b, 0xe2, 0xf1, 0x1a, 0x70, 0x76, 0x3c, 0x2e, 0x7f, 0x3f, 0x3b, 0x7b, 0x66, 0xa3, 0x4b, 0x1b, 0x5c, 0x0f, 0xbe, 0xdd, 0x98, 0x5a, 0x5b, 0xd0, 0x0a, 0x3d, 0x7e, 0x2c, 0x10, 0x56, 0x2a, 0x10, 0x87, 0x5d, 0xd9, 0xb9, 0x7f, 0x3e, 0x2e, 0x86, 0xb7, 0x17, 0x04, 0xdf, 0xb1, 0x27, 0xc4, 0x47, 0xe2, 0xd9, 0x7a, 0x9a, 0x48, 0x7c, 0xdb, 0xc6, 0x1d, 0x3c, 0x00, 0xa3, 0x21 def dump(n, a):
def byteswap(v):
return ((v & 0xff) << 24) | ((v & 0xff00) << 8) | ((v & 0xff0000) >> 8) | ((v & 0xff000000) >> 24)
def rol4(n, m):
return ((n << m) | (n >> (32 - m))) & 0xffffffff
def ror4(n, m):
return ((n >> m) | (n << (32 - m))) & 0xffffffff
def tnls(a1):
a3 = 0
for i in range(0, 32, 8):
return a3
def kls(a1):
a3 = a1
a3 ^= rol4(a1, 11)
a3 ^= ror4(a1, 7)
return a3
def els(a1):
a3 = a1
a3 ^= rol4(a1, 3)
a3 ^= rol4(a1, 14)
a3 ^= rol4(a1, 15)
a3 ^= rol4(a1, 9)
return a3
def ks(a1):
return kls(tnls(a1))
def es(a1):
return els(tnls(a1))
def r(a1, a2):
return es(a2 ^ a11 ^ a12 ^ a13) ^ a10 def encrypt_block(msg_blocks, key):
v37 = []
for i in range(4):
v37.append(byteswap(msg_blocksi)) dump('v37', v37)
for i in range(32):
print('v5', hex(v5))
dump('v37', v37)
v28 = []
for i in range(4):
v28.append(byteswap(v373 - i)) dump('v28', v28)
return v28
def encrypt(msg, key):
v8 = []
for i in range(4):
v8.append(fishi ^ byteswap(keyi)) dump('v8', v8)
key2 = []
for i in range(32):
v11 = ks(cati ^ v83 ^ v82 ^ v81) ^ v80 key2.append(v11)
dump('key2', key2)
enc_msg = []
for j in range(0, len(msg), 16):
msg_blocks = []
for i in range(0, 16, 4):
dump('msg_blocks', msg_blocks)
enc_msg_blocks = encrypt_block(msg_blocks, key2)
dump('enc_msg_blocks', enc_msg_blocks)
for i in range(len(enc_msg_blocks)):
enc_msg.append(enc_msg_blocksi & 0xff) enc_msg.append((enc_msg_blocksi >> 8) & 0xff) enc_msg.append((enc_msg_blocksi >> 16) & 0xff) enc_msg.append((enc_msg_blocksi >> 24) & 0xff) return enc_msg
def main():
msg = input().encode()
pad_length = 16 - (len(msg) % 16)
msg += chr(pad_length).encode() * pad_length
dump('msg', msg)
enc_msg = encrypt(msg, key)
dump('enc_msg', enc_msg)
main()
バイナリから暗号アルゴリズム、暗号化に使われた鍵、暗号化されたflagがわかるため、適切に復号することでflagが得られた。
code:python
def decrypt_block(enc_msg_blocks, key):
v37 = []
for i in range(4):
v37.append(byteswap(enc_msg_blocks3 - i)) dump('v37', v37)
for i in reversed(range(32)):
dump('v37', v37)
msg_blocks = []
for i in range(4):
msg_blocks.append(byteswap(v37i)) return msg_blocks
def decrypt(enc_msg, key):
v8 = []
for i in range(4):
v8.append(fishi ^ byteswap(keyi)) dump('v8', v8)
key2 = []
for i in range(32):
v11 = ks(cati ^ v83 ^ v82 ^ v81) ^ v80 key2.append(v11)
dump('key2', key2)
msg = []
for j in range(0, len(enc_msg), 16):
enc_msg_blocks = []
for i in range(0, 16, 4):
dump('enc_msg_blocks', enc_msg_blocks)
msg_blocks = decrypt_block(enc_msg_blocks, key2)
dump('msg_blocks', msg_blocks)
for i in range(len(msg_blocks)):
msg.append(msg_blocksi & 0xff) msg.append((msg_blocksi >> 8) & 0xff) msg.append((msg_blocksi >> 16) & 0xff) msg.append((msg_blocksi >> 24) & 0xff) return msg
def main():
msg = decrypt(enc, key)
main()