add premium rsa, not sure if autogen will work

premium-rsa/description.md

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+My RSA is the greatest. It's so strong, in fact, that I'll even give you d! [file](${ciphertext_txt})

premium-rsa/grader.py

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+from cStringIO import StringIO
+import os, random
+from Crypto.Util import number
+
+flag = randleetify("i_probably_shouldnta_leeked_d",random)
+
+def egcd(a, b):
+    if a == 0:
+        return (b, 0, 1)
+    else:
+        g, y, x = egcd(b % a, a)
+        return (g, x - (b // a) * y, y)
+
+def modinv(a, m):
+    g, x, y = egcd(a, m)
+    if g != 1:
+        raise Exception('modular inverse does not exist')
+    else:
+        return x % m
+
+def randleetify(s, random):
+    i = list(s)
+    for c in range(len(i)):
+        if random.random() > 0.5:
+            if i[c] == 'i':
+                if random.random() > 0.66:
+                    i[c] = '1'
+                elif random.random() > 0.33:
+                    i[c] = 'I'
+            elif i[c] == 'o':
+                if random.random() > 0.66:
+                    i[c] = '0'
+                elif random.random() > 0.33:
+                    i[c] = 'O'
+            elif i[c] == 'a':
+                if random.random() > 0.66:
+                    i[c] = '4'
+                elif random.random() > 0.33:
+                    i[c] = 'A'
+            elif i[c] == 'l':
+                if random.random() > 0.66:
+                    i[c] = '1'
+                elif random.random() > 0.33:
+                    i[c] = 'L'
+            elif i[c] == 's':
+                if random.random() > 0.66:
+                    i[c] = '5'
+                elif random.random() > 0.33:
+                    i[c] = 'S'
+            elif i[c] == 'e':
+                if random.random() > 0.66:
+                    i[c] = '3'
+                elif random.random() > 0.33:
+                    i[c] = 'E'
+            elif i[c].isalpha():
+                if random.random() > 0.5:
+                    i[c] = i[c].upper()
+        return ''.join(i)
+
+
+def get_problem(random):
+    n_length = 2048
+
+    p = number.getPrime(n_length, os.urandom)
+    q = number.getPrime(n_length, os.urandom)
+    n = p*q
+    e = 65537
+    phi = (p-1)*(q-1)
+    d = modinv(e, phi)
+    cut = len(bin(d).strip('0b').strip('L'))//2
+    given = bin(d).strip('0b').strip('L')[cut:]
+    deez = hex(int(given,2)).zfill(len(given)/4)
+    salt = random.choice("!?.")
+    return (n, e, cut, deez, salt)
+
+def generate_ciphertext(random):
+    n, e, cut, deez, salt = get_problem(random)
+    encoded = int(("easyctf{%s%s}" % (flag, salt)).encode('hex'),16)
+    ciphertext =  'n: '+str(n)+'\n'
+    ciphertext += 'e: '+str(e)+'\n'
+    ciphertext += 'd: [??? '+str(cut)+' REDACTED BITS ???]'+str(deez)+'\n'
+    ciphertext += 'c: '+str(pow(encoded, e, n))+'\n'
+
+    return StringIO(ciphertext)
+
+def generate(random):
+    return dict(files={
+        "ciphertext.txt": generate_ciphertext
+    })
+
+def grade(random, key):
+    n, e, deez, salt = get_problem(random)
+    if key.find("%s_%s" % (flag, salt)) >= 0:
+        return True, "Correct!"
+    return False, "Nope."

premium-rsa/problem.yml

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+title: Premium RSA
+author: neptunia
+hint: You thought it'd be that simple?
+category: Cryptography
+autogen: true
+programming: false
+value: 350