OTA firmware MD5 check + password support for esp-idf (#2507)

Co-authored-by: Maurice Makaay <account-github@makaay.nl>

esphome/components/md5/md5.cpp

@@ -0,0 +1,51 @@
+#include <cstdio>
+#include <cstring>
+#include "md5.h"
+#include "esphome/core/helpers.h"
+
+namespace esphome {
+namespace md5 {
+
+void MD5Digest::init() {
+  memset(this->digest_, 0, 16);
+  MD5Init(&this->ctx_);
+}
+
+void MD5Digest::add(const uint8_t *data, size_t len) { MD5Update(&this->ctx_, data, len); }
+
+void MD5Digest::calculate() { MD5Final(this->digest_, &this->ctx_); }
+
+void MD5Digest::get_bytes(uint8_t *output) { memcpy(output, this->digest_, 16); }
+
+void MD5Digest::get_hex(char *output) {
+  for (size_t i = 0; i < 16; i++) {
+    sprintf(output + i * 2, "%02x", this->digest_[i]);
+  }
+}
+
+bool MD5Digest::equals_bytes(const char *expected) {
+  for (size_t i = 0; i < 16; i++) {
+    if (expected[i] != this->digest_[i]) {
+      return false;
+    }
+  }
+  return true;
+}
+
+bool MD5Digest::equals_hex(const char *expected) {
+  for (size_t i = 0; i < 16; i++) {
+    auto high = parse_hex(expected[i * 2]);
+    auto low = parse_hex(expected[i * 2 + 1]);
+    if (!high.has_value() || !low.has_value()) {
+      return false;
+    }
+    auto value = (*high << 4) | *low;
+    if (value != this->digest_[i]) {
+      return false;
+    }
+  }
+  return true;
+}
+
+}  // namespace md5
+}  // namespace esphome