1 files changed, 110 insertions, 0 deletions
diff --git a/src/crypto/electrum-words.cpp b/src/crypto/electrum-words.cpp
new file mode 100644
index 000000000..96a392d04
--- /dev/null
+++ b/src/crypto/electrum-words.cpp
@@ -0,0 +1,110 @@
+/*
+ * This file and its header file are for translating Electrum-style word lists
+ * into their equivalent byte representations for cross-compatibility with
+ * that method of "backing up" one's wallet keys.
+ */
+
+#include <string>
+#include <cassert>
+#include <map>
+#include <cstdint>
+#include <vector>
+#include <boost/algorithm/string.hpp>
+#include "crypto/crypto.h"  // for declaration of crypto::secret_key
+
+#include "crypto/electrum-words.h"
+
+namespace crypto
+{
+  namespace ElectrumWords
+  {
+
+    /* convert words to bytes, 3 words -> 4 bytes
+     * returns:
+     *    false if not a multiple of 3 words, or if a words is not in the
+     *    words list
+     *
+     *    true otherwise
+     */
+    bool words_to_bytes(const std::string& words, crypto::secret_key& dst)
+    {
+      int n = NUMWORDS; // hardcoded because this is what electrum uses
+
+      std::vector<std::string> wlist;
+
+      boost::split(wlist, words, boost::is_any_of(" "));
+
+      // error on non-compliant word list
+      if (wlist.size() != 12 && wlist.size() != 24) return false;
+
+      for (unsigned int i=0; i < wlist.size() / 3; i++)
+      {
+        uint32_t val;
+        uint32_t w1, w2, w3;
+
+        // verify all three words exist in the word list
+        if (wordsMap.count(wlist[i*3]) == 0 ||
+            wordsMap.count(wlist[i*3 + 1]) == 0 ||
+            wordsMap.count(wlist[i*3 + 2]) == 0)
+        {
+          return false;
+        }
+
+        w1 = wordsMap.at(wlist[i*3]);
+        w2 = wordsMap.at(wlist[i*3 + 1]);
+        w3 = wordsMap.at(wlist[i*3 + 2]);
+
+        val = w1 + n * (((n - w1) + w2) % n) + n * n * (((n - w2) + w3) % n);
+
+        if (!(val % n == w1)) return false;
+
+        memcpy(dst.data + i * 4, &val, 4);  // copy 4 bytes to position
+      }
+
+      std::string wlist_copy = words;
+      if (wlist.size() == 12)
+      {
+        memcpy(dst.data, dst.data + 16, 16);  // if electrum 12-word seed, duplicate
+        wlist_copy += ' ';
+        wlist_copy += words;
+      }
+
+      return true;
+    }
+
+    /* convert bytes to words, 4 bytes-> 3 words
+     * returns:
+     *    false if wrong number of bytes (shouldn't be possible)
+     *    true otherwise
+     */
+    bool bytes_to_words(const crypto::secret_key& src, std::string& words)
+    {
+      int n = NUMWORDS; // hardcoded because this is what electrum uses
+
+      if (sizeof(src.data) % 4 != 0) return false;
+
+      // 8 bytes -> 3 words.  8 digits base 16 -> 3 digits base 1626
+      for (unsigned int i=0; i < sizeof(src.data)/4; i++, words += ' ')
+      {
+        uint32_t w1, w2, w3;
+        
+        uint32_t val;
+
+        memcpy(&val, (src.data) + (i * 4), 4);
+
+        w1 = val % n;
+        w2 = ((val / n) + w1) % n;
+        w3 = (((val / n) / n) + w2) % n;
+
+        words += wordsArray[w1];
+        words += ' ';
+        words += wordsArray[w2];
+        words += ' ';
+        words += wordsArray[w3];
+      }
+      return false;
+    }
+
+  }  // namespace ElectrumWords
+
+}  // namespace crypto