Fractured Seal

CACTF2026

Task: an RSA-2048 PKCS#1 private-key PEM is heavily redacted with '*' but keeps position-preserving base64 alignment, plus a ciphertext. Solution: decode each intact 4-char base64 group at its fixed DER offset to recover 576 high bits of a prime factor and all but the low byte of n, then factor n via Coppersmith known-high-bits (LLL) while brute-forcing the 128 odd candidate low bytes of n.