Data commit

Task/RSA-code/Nim/rsa-code.nim

@@ -0,0 +1,50 @@
+import strutils, streams, strformat
+# nimble install stint
+import stint
+
+const messages = ["PPAP", "I have a pen, I have a apple\nUh! Apple-pen!",
+    "I have a pen, I have pineapple\nUh! Pineapple-pen!",
+    "Apple-pen, pineapple-pen\nUh! Pen-pineapple-apple-pen\nPen-pineapple-apple-pen\nDance time!", "\a\0"]
+const
+  n = u256("9516311845790656153499716760847001433441357")
+  e = u256("65537")
+  d = u256("5617843187844953170308463622230283376298685")
+proc pcount(s: string, c: char): int{.inline.} =
+  for ch in s:
+    if ch != c:
+      break
+    result+=1
+func powmodHexStr(s: string, key, divisor: UInt256): string{.inline.} =
+  toHex(powmod(UInt256.fromHex(s), key, divisor))
+proc translate(hexString: string, key, divisor: UInt256,
+    encrypt = true): string =
+  var
+    strm = newStringStream(hexString)
+    chunk, residue, tempChunk: string
+  let chunkSize = len(toHex(divisor))
+  while true:
+    tempChunk = strm.peekStr(chunkSize-int(encrypt)*3)
+    if len(chunk) > 0:
+      if len(tempChunk) == 0:
+        if encrypt:
+          result&=powmodHexStr(pcount(chunk, '0').toHex(2)&align(chunk,
+              chunkSize-3, '0'), key, divisor)
+        else:
+          tempChunk = align(powmodHexStr(chunk, key, divisor), chunkSize-1, '0')
+          residue = tempChunk[2..^1].strip(trailing = false, chars = {'0'})
+          result&=align(residue, fromHex[int](tempChunk[0..1])+len(residue), '0')
+        break
+      result&=align(powmodHexStr(chunk, key, divisor), chunkSize-3+int(
+          encrypt)*3, '0')
+    discard strm.readStr(chunkSize-int(encrypt)*3)
+    chunk = tempChunk
+  strm.close()
+for message in messages:
+  echo(&"plaintext:\n{message}")
+  var numPlaintext = message.toHex()
+  echo(&"numerical plaintext in hex:\n{numPlaintext}")
+  var ciphertext = translate(numPlaintext, e, n)
+  echo(&"ciphertext is: \n{ciphertext}")
+  var deciphertext = translate(ciphertext, d, n, false)
+  echo(&"deciphered numerical plaintext in hex is:\n{deciphertext}")
+  echo(&"deciphered plaintext is:\n{parseHexStr(deciphertext)}\n\n")