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# ================= GF(2^8) =================
def gf_mul(a, b):
res = 0
for _ in range(8):
if b & 1:
res ^= a
hi = a & 0x80
a = (a << 1) & 0xFF
if hi:
a ^= 0x1B
b >>= 1
return res
def gf_pow254(x):
if x == 0:
return 0
y = 1
for _ in range(253):
y = gf_mul(y, x)
return y
def rol8(x, n):
return ((x << n) | (x >> (8-n))) & 0xFF
# ================= 构建 SBox 和逆 SBox =================
def build_sbox():
s = []
for i in range(256):
inv = gf_pow254(i)
y = inv ^ rol8(inv,1) ^ rol8(inv,2) ^ rol8(inv,3) ^ rol8(inv,4)
y ^= 0x30
s.append(y)
return s
SBOX = build_sbox()
INV_SBOX = [0]*256
for i, val in enumerate(SBOX):
INV_SBOX[val] = i
# ================= key schedule =================
RCON = [ord(c) for c in "easypython?"] # 11 bytes
def key_expand(key16: bytes):
w = list(key16)
for j in range(4, 44):
t0, t1, t2, t3 = w[4*j-4:4*j]
if j % 4 == 0:
t0, t1, t2, t3 = t1, t2, t3, t0
t0, t1, t2, t3 = SBOX[t0], SBOX[t1], SBOX[t2], SBOX[t3]
t0 ^= RCON[j//4]
for k, t in enumerate([t0, t1, t2, t3]):
w.append(w[4*(j-4)+k] ^ t)
return w # 176 bytes
# ================= AES 基本操作 =================
def add_round_key(round_id, state, rk):
for i in range(4):
for j in range(4):
state[4*i+j] ^= rk[16*round_id + 4*i + j]
def sub_bytes(state):
for i in range(4):
for j in range(4):
state[4*j+i] = SBOX[state[4*j+i]]
def inv_sub_bytes(state):
for i in range(4):
for j in range(4):
state[4*j+i] = INV_SBOX[state[4*j+i]]
def shift_rows(s):
s[1], s[5], s[9], s[13] = s[5], s[9], s[13], s[1]
s[2], s[10] = s[10], s[2]
s[6], s[14] = s[14], s[6]
s[3], s[15], s[11], s[7] = s[15], s[11], s[7], s[3]
def inv_shift_rows(s):
# 第1行右移1 (即左移3)
s[1], s[5], s[9], s[13] = s[13], s[1], s[5], s[9]
# 第2行右移2 (自逆)
s[2], s[10] = s[10], s[2]
s[6], s[14] = s[14], s[6]
# 第3行右移1 (即左移1)
s[3], s[7], s[11], s[15] = s[7], s[11], s[15], s[3]
def xtime(x):
return ((x<<1) & 0xFF) ^ (0x1B if (x & 0x80) else 0)
def mix_columns(s):
for i in range(4):
a0, a1, a2, a3 = s[4*i:4*i+4]
t = a0 ^ a1 ^ a2 ^ a3
u = a0
s[4*i+0] ^= t ^ xtime(a0 ^ a1)
s[4*i+1] ^= t ^ xtime(a1 ^ a2)
s[4*i+2] ^= t ^ xtime(a2 ^ a3)
s[4*i+3] ^= t ^ xtime(a3 ^ u)
def inv_mix_columns(s):
for i in range(4):
a0, a1, a2, a3 = s[4*i:4*i+4]
b0 = gf_mul(a0, 0x0e) ^ gf_mul(a1, 0x0b) ^ gf_mul(a2, 0x0d) ^ gf_mul(a3, 0x09)
b1 = gf_mul(a0, 0x09) ^ gf_mul(a1, 0x0e) ^ gf_mul(a2, 0x0b) ^ gf_mul(a3, 0x0d)
b2 = gf_mul(a0, 0x0d) ^ gf_mul(a1, 0x09) ^ gf_mul(a2, 0x0e) ^ gf_mul(a3, 0x0b)
b3 = gf_mul(a0, 0x0b) ^ gf_mul(a1, 0x0d) ^ gf_mul(a2, 0x09) ^ gf_mul(a3, 0x0e)
s[4*i:4*i+4] = [b0, b1, b2, b3]
def aes_encrypt_block(state, w):
add_round_key(0, state, w)
for r in range(1, 10):
sub_bytes(state)
shift_rows(state)
mix_columns(state)
add_round_key(r, state, w)
sub_bytes(state)
shift_rows(state)
add_round_key(10, state, w)
def aes_decrypt_block(state, w):
add_round_key(10, state, w)
for r in range(9, 0, -1):
inv_shift_rows(state)
inv_sub_bytes(state)
add_round_key(r, state, w)
inv_mix_columns(state)
inv_shift_rows(state)
inv_sub_bytes(state)
add_round_key(0, state, w)
# ================= 解密主函数 =================
KEY = b"nice_to_meet_you"
IV = b"1145141145144332"
def decrypt_48(cipher_hex: str):
cipher = bytes.fromhex(cipher_hex)
assert len(cipher) == 48
w = key_expand(KEY)
iv = list(IV) # 初始IV
plain = bytearray()
for i in range(0, 48, 16):
block = list(cipher[i:i+16])
state = block[:] # 密文块
aes_decrypt_block(state, w) # state 现在为中间值 = 明文 ^ iv ^ 0x33
# 恢复明文
for j in range(16):
state[j] ^= iv[j] ^ 0x33
plain.extend(state)
iv = block # 下一个IV用当前密文块（原始密文）
return bytes(plain)
# ================= 执行解密 =================
if __name__ == "__main__":
cipher_hex = "4245E97D2232F72C3DCA15F74FCC844BDEADB951CF29CDE2336060A62C034F551174A4D805F4AC44BA204B8600269074"
plain = decrypt_48(cipher_hex)
print("解密结果（十六进制）:", plain.hex())
try:
print("解密结果（UTF-8）:", plain.decode('utf-8'))
except:
print("解密结果（原始字节）:", plain)
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