From f4a3bef33294814193d3433dcddec117e9ac73c7 Mon Sep 17 00:00:00 2001
From: Thomas Schmucker <ts@its1.de>
Date: Tue, 25 Aug 2020 17:08:00 +0200
Subject: Beispiel für bcrypt hinzugefügt
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---
 bcrypt-test.c | 96 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 95 insertions(+), 1 deletion(-)

diff --git a/bcrypt-test.c b/bcrypt-test.c
index b09dee6..2bbdfe7 100644
--- a/bcrypt-test.c
+++ b/bcrypt-test.c
@@ -1,11 +1,105 @@
 #include <stdio.h>
 #include <stdlib.h>
+#include <stdbool.h>
+#include <ctype.h>
+#include <string.h>
 
 #include "lua-bcrypt/compat/include/pwd.h"
 
+#define USER_DATABASE "./user.db"
+#define SECURITY_LEVEL 12
+
+static bool
+valid_char(int ch)
+{
+	return isalnum(ch) || ch == '_' || ch == '-' || ch == '.';
+}
+
+/**
+ * Create a new user/password
+ *
+ * \param[in] username
+ * \param[in] password
+ *
+ * \return true on success (user was created) or false on error
+ */
+bool
+create_user(const char *username, const char *password)
+{
+	// check for invalid characters in username
+	for ( const char *ptr = username; *ptr; ++ptr ) {
+		if ( !valid_char(*ptr) ) {
+			return false;
+		}
+	}
+
+	FILE *db = fopen(USER_DATABASE, "a");
+	if ( db == NULL ) {
+		return false;
+	}
+
+	char hash[_PASSWORD_LEN + 1] = { 0 };
+
+	if ( bcrypt_newhash(password, SECURITY_LEVEL, hash, _PASSWORD_LEN) != 0 ) {
+		return false;
+	}
+
+	fprintf(db, "%s|%s\n", username, hash);
+	fclose(db);
+
+	return true;
+}
+
+/**
+ * Check is a valid username/password exists in the user-database
+ *
+ * \param[in] username
+ * \param[in] password
+ *
+ * \return true, if the user was successfully authenticated, otherwise false
+ */
+bool
+check_user(const char *username, const char *password)
+{
+	FILE *db = fopen(USER_DATABASE, "r");
+	if ( db == NULL ) {
+		return false;
+	}
+
+	const size_t username_length = strlen(username);
+	char line[256];
+
+	bool found = false;
+	while ( !found && fgets(line, sizeof line, db) ) {
+		line[strcspn(line, "\r\n")] = '\0'; // remove newline (if exists)
+
+		if ( strncmp(line, username, username_length) != 0 ) {
+			continue;
+		}
+
+		if ( line[username_length] != '|' ) {
+			continue;
+		}
+
+		if ( bcrypt_checkpass(password, &line[username_length+1]) != 0 ) {
+			continue;
+		}
+
+		// User successfully authenticated!
+		found = true;
+	}
+
+	fclose(db);
+
+	return found;
+}
+
 int
 main(void)
 {
-	puts("Hallo Welt...");
+	if ( check_user("Thomas", "Passwort") ) {
+		puts("Benutzer erfolgreich überprüft!");
+	}
+
 	return EXIT_SUCCESS;
 }
-- 
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