1 files changed, 49 insertions, 0 deletions
diff --git a/challenge-016/archargelod/nim/ch_2.nim b/challenge-016/archargelod/nim/ch_2.nim
new file mode 100755
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+++ b/challenge-016/archargelod/nim/ch_2.nim
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+#!/usr/bin/env -S nim r -d:release --verbosity:0 --hints:off
+import std/strutils
+import pkg/nimcrypto/sha2 ## `$ nimble install nimcrypto`
+
+const
+  DecodedLength = 25
+  ChecksumLength = 4
+
+func base58Decode(input: string): array[DecodedLength, byte] =
+  ## Taken from https://rosettacode.org/wiki/Bitcoin/address_validation#Nim
+  ## Tried to implement this myself, but failed to find easy to understand algorithm.
+  const Base = "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz"
+
+  for c in input:
+    var n = Base.find(c)
+    if n < 0:
+      raise newException(ValueError, "invalid character: " & c)
+
+    for i in countdown(result.high, 0):
+      n += Base.len * result[i].int
+      result[i] = byte(n and 255)
+      n = n div 256
+
+    if n != 0:
+      raise newException(ValueError, "decoded address is too long")
+
+func validBtcChecksum(address: openarray[byte]): bool =
+  let digest1 = sha256.digest(address.toOpenArray(0, address.high - ChecksumLength)).data
+  let digest2 = sha256.digest(digest1).data
+  digest2[0 ..< ChecksumLength] == address[^ChecksumLength ..^ 1]
+
+func isValidBTCAddress(address: string): bool =
+  address.len >= 26 and address[0] in {'1', '3'} and
+    validBtcChecksum(address.base58Decode())
+
+when isMainModule:
+  import std/unittest
+
+  const
+    Valid = ["1BvBMSEYstWetqTFn5Au4m4GFg7xJaNVN2", "3J98t1WpEZ73CNmQviecrnyiWrnqRhWNLy"]
+    Invalid = ["3J98t1WpEZ73CNmQviecrnyiWrDEADBEEF"]
+
+  suite "Validate bitcoin address":
+    test "Example 1":
+      check isValidBTCAddress Valid[0]
+    test "Example 2":
+      check isValidBTCAddress Valid[1]
+    test "Invalid address":
+      check not isValidBtcAddress Invalid[0]