docbody = [206,56,8,128,209,47,2,149,202,34,95,128,226,41,92,156,
           142,38,51,153,137,57,51,218,211,21,88,130,201,121,30,128,
           137,62,93,152,142,55]

prefix = "srdn"

key = []
for i, c in enumerate(prefix):
    key.append(docbody[i] ^ ord(c))

print(f"Derived key bytes: {key}")
print(f"Derived key chars: {''.join(chr(k) for k in key)}")

# Decode full docbody with cycling key
result = ''.join(chr(docbody[i] ^ key[i % len(key)]) for i in range(len(docbody)))
print(f"\nDecoded flag: {result}")