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Task/Vigen-re-cipher/D/vigen-re-cipher.d

@@ -0,0 +1,29 @@
+import std.stdio, std.string;
+
+string encrypt(in string txt, in string key) pure
+in {
+    assert(key.removechars("^A-Z") == key);
+} body {
+    string res;
+    foreach (immutable i, immutable c; toUpper(txt).removechars("^A-Z"))
+        res ~= (c + key[i % $] - 2 * 'A') % 26 + 'A';
+    return res;
+}
+
+string decrypt(in string txt, in string key) pure
+in {
+    assert(key.removechars("^A-Z") == key);
+} body {
+    string res;
+    foreach (immutable i, immutable c; toUpper(txt).removechars("^A-Z"))
+       res ~= (c - key[i % $] + 26) % 26 + 'A';
+    return res;
+}
+
+void main() {
+    immutable key = "VIGENERECIPHER";
+    immutable original = "Beware the Jabberwock, my son!" ~
+                         " The jaws that bite, the claws that catch!";
+    immutable encoded = original.encrypt(key);
+    writeln(encoded, "\n", encoded.decrypt(key));
+}