From 4ba7f6bf14c2d98512996967d2c747f0733b7e83 Mon Sep 17 00:00:00 2001
From: Matthew Gretton-Dann <matt@gretton-dann.org.uk>
Date: Fri, 3 Dec 2021 17:13:37 +0000
Subject: [PATCH] Add 2016 Day 5 puzzles

---
 2016/puzzle-05-01.CMakeLists.txt |  2 ++
 2016/puzzle-05-01.cc             | 59 ++++++++++++++++++++++++++++++++
 2016/puzzle-05-02.CMakeLists.txt |  2 ++
 2016/puzzle-05-02.cc             | 56 ++++++++++++++++++++++++++++++
 4 files changed, 119 insertions(+)
 create mode 100644 2016/puzzle-05-01.CMakeLists.txt
 create mode 100644 2016/puzzle-05-01.cc
 create mode 100644 2016/puzzle-05-02.CMakeLists.txt
 create mode 100644 2016/puzzle-05-02.cc

diff --git a/2016/puzzle-05-01.CMakeLists.txt b/2016/puzzle-05-01.CMakeLists.txt
new file mode 100644
index 0000000..1f298ff
--- /dev/null
+++ b/2016/puzzle-05-01.CMakeLists.txt
@@ -0,0 +1,2 @@
+find_package(OpenSSL REQUIRED)
+target_link_libraries("${puzzle_name}" OpenSSL::SSL)
diff --git a/2016/puzzle-05-01.cc b/2016/puzzle-05-01.cc
new file mode 100644
index 0000000..b9d66bc
--- /dev/null
+++ b/2016/puzzle-05-01.cc
@@ -0,0 +1,59 @@
+#include <algorithm>
+#include <array>
+#include <cassert>
+#include <iostream>
+#include <string>
+
+#include <openssl/evp.h>
+
+using MD5Digest = std::array<unsigned char, EVP_MAX_MD_SIZE>;
+
+auto md5(MD5Digest& digest, std::string const& s) -> unsigned int
+{
+  EVP_MD const* md{EVP_md5()};
+  unsigned int md_len{0};
+
+  EVP_MD_CTX* md_context{EVP_MD_CTX_new()};
+  assert(md_context != nullptr);
+  EVP_DigestInit_ex2(md_context, md, nullptr);
+  EVP_DigestUpdate(md_context, s.data(), s.length());
+  EVP_DigestFinal_ex(md_context, digest.data(), &md_len);
+  return md_len;
+}
+
+auto get_letter(std::string const& s) -> unsigned
+{
+  MD5Digest digest;
+  auto len = md5(digest, s);
+  assert(len >= 3);
+  if (digest[0] == 0 && digest[1] == 0 && (digest[2] & 0xf0) == 0) {
+    return digest[2] & 0xf;
+  }
+  return 16;
+}
+
+auto main() -> int
+{
+  constexpr std::string_view characters{"0123456789abcdef"};
+  constexpr unsigned password_length{8};
+
+  std::string result;
+  std::string line;
+  if (!std::getline(std::cin, line)) {
+    std::cerr << "Unable to read from stdin.\n";
+    return 1;
+  }
+
+  std::uint64_t i{0};
+  for (unsigned letter = 0; letter < password_length; ++letter) {
+    unsigned c{0};
+    while ((c = get_letter(line + std::to_string(i))) == 16) {
+      ++i;
+    }
+    result += characters.at(c);
+    ++i;
+  }
+
+  std::cout << "Password: " << result << '\n';
+  return 0;
+}
\ No newline at end of file
diff --git a/2016/puzzle-05-02.CMakeLists.txt b/2016/puzzle-05-02.CMakeLists.txt
new file mode 100644
index 0000000..1f298ff
--- /dev/null
+++ b/2016/puzzle-05-02.CMakeLists.txt
@@ -0,0 +1,2 @@
+find_package(OpenSSL REQUIRED)
+target_link_libraries("${puzzle_name}" OpenSSL::SSL)
diff --git a/2016/puzzle-05-02.cc b/2016/puzzle-05-02.cc
new file mode 100644
index 0000000..374dc5c
--- /dev/null
+++ b/2016/puzzle-05-02.cc
@@ -0,0 +1,56 @@
+#include <algorithm>
+#include <array>
+#include <cassert>
+#include <iostream>
+#include <string>
+
+#include <openssl/evp.h>
+
+using MD5Digest = std::array<unsigned char, EVP_MAX_MD_SIZE>;
+
+auto md5(MD5Digest& digest, std::string const& s) -> unsigned int
+{
+  EVP_MD const* md{EVP_md5()};
+  unsigned int md_len{0};
+
+  EVP_MD_CTX* md_context{EVP_MD_CTX_new()};
+  assert(md_context != nullptr);
+  EVP_DigestInit_ex2(md_context, md, nullptr);
+  EVP_DigestUpdate(md_context, s.data(), s.length());
+  EVP_DigestFinal_ex(md_context, digest.data(), &md_len);
+  return md_len;
+}
+
+auto main() -> int
+{
+  constexpr std::string_view characters{"0123456789abcdef"};
+  constexpr unsigned password_length{8};
+
+  std::string result{"--------"};
+  std::string line;
+  if (!std::getline(std::cin, line)) {
+    std::cerr << "Unable to read from stdin.\n";
+    return 1;
+  }
+
+  std::uint64_t i{0};
+  while (std::any_of(result.begin(), result.end(), [](char c) { return c == '-'; })) {
+    MD5Digest digest;
+    auto len = md5(digest, line + std::to_string(i));
+    assert(len >= 3);
+    if (digest[0] == 0 && digest[1] == 0 && (digest[2] & 0xf0) == 0) {
+      auto idx{digest[2] & 0xf};
+      if (idx < password_length) {
+        if (result.at(idx) == '-') {
+          result[idx] = characters[(digest[3] & 0xf0) >> 4];
+          std::cout << '\n';
+        }
+      }
+    }
+    std::cout << '\r' << result << ' ' << line << i << std::flush;
+    ++i;
+  }
+
+  std::cout << "\nPassword: " << result << '\n';
+  return 0;
+}
\ No newline at end of file