Sum-O-Primes

sum_o_primes/gen.py

@@ -0,0 +1,37 @@
+#!python3
+
+from binascii import hexlify
+from gmpy2 import mpz_urandomb, next_prime, random_state
+import math
+import os
+import sys
+
+if sys.version_info < (3, 9):
+    import gmpy2
+    math.gcd = gmpy2.gcd
+    math.lcm = gmpy2.lcm
+
+FLAG  = open('flag.txt').read().strip()
+FLAG  = int(hexlify(FLAG.encode()), 16)
+SEED  = int(hexlify(os.urandom(32)).decode(), 16)
+STATE = random_state(SEED)
+
+def get_prime(bits):
+    return next_prime(mpz_urandomb(STATE, bits) | (1 << (bits - 1)))
+
+p = get_prime(1024)
+q = get_prime(1024)
+
+x = p + q
+n = p * q
+
+e = 65537
+
+m = math.lcm(p - 1, q - 1)
+d = pow(e, -1, m)
+
+c = pow(FLAG, e, n)
+
+print(f'x = {x:x}')
+print(f'n = {n:x}')
+print(f'c = {c:x}')

sum_o_primes/output.txt

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+x = 1429cf99b5dd5dde9f016095be650d5b0a9a73e648aa72324cb8eb05bd14c1b913539a97f5417474f6014de830ad6dee028dd8908e593b1e99c4cc88f400127214036e71112292e58a2ccffc48f57524aee90f9858d935c7a86297a90c7fe48b80f6c4e8df9eaae501ef40da7984502457255fbc8a9e1574ec6ba210be134f192
+n = 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
+c = 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

sum_o_primes/sol.py

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+#!python3
+from sage.all import *
+import pwn
+
+with open("output.txt", 'r') as f:
+    lines = f.readlines()
+    x = Integer(lines[0][4:], 16)
+    N = Integer(lines[1][4:], 16)
+    c = Integer(lines[2][4:], 16)
+
+pwn.log.info("x: {}".format(x))
+pwn.log.info("N: {}".format(N))
+pwn.log.info("c: {}".format(c))
+
+# n = p*q
+# x = p+q
+# -> n = p*(x-p)
+# -> n = px - p²
+# -> p² - px + n = 0
+# -> (p - x/2)² + n - x²/4 = 0
+# -> (p - x/2)² = x²/4 - n
+# -> p - x/2 = +- sqrt(x²/4 - n)
+# -> p = x/2 +- sqrt(x²/4 - n)
+
+disc = sqrt(pow(x, 2)//4 - N)
+p = x//2 + disc
+q = x//2 - disc
+# since (p, q) can be replaced by (q, p)
+assert p+q == x
+assert p*q == N
+pwn.log.success("calculated p and q")
+pwn.log.info("p: {}".format(p))
+pwn.log.info("q: {}".format(q))
+
+e = Integer(65537)
+d = pow(e, -1, (p-1)*(q-1))
+pwn.log.info("calculated d: {}".format(d))
+
+m = pow(c, d, N)
+m_literal = pwn.pack(int(m), 'all', 'big', False)
+pwn.log.success(m_literal.decode())
+