Indice dei contenuti
L'algoritmo di cifratura AES 256 / Rijndael vanta già numerose implementazioni in ambito ASP.NET C#: progetti come BouncyCastle, SharpAESCrypt e CryptoN, solo per menzionare alcuni tra i più noti e diffusi, sono molto semplici da utilizzare e funzionano alla perfezione. Che bisogno c'è, dunque, di realizzare un'ennesima libreria di data-encryption AES 256 C#?
La risposta è grossomodo la stessa che normalmente diamo quando ci tocca, nostro malgrado, "reinventare la ruota"; è la medesima ragione che ci ha spinto a realizzare il nostro generatore di password casuali in C#, il convertitore PDF-to-TXT e PDF-to-HTML e molte altre classi helper per C#, PHP e altri linguaggi di programmazione back-end: avevamo bisogno di fare qualcosa che non era possibile fare con le alternative open-source già esistenti. Questa volta avevamo la necessità di configurare alcuni aspetti particolarmente avanzati dell'algoritmo di cifratura AES, o meglio di avere la possibilità di poterli modificare a nostro piacimento per poterli adattare alle varie librerie utilizzate dai nostri clienti e, in massima parte, ben poco "configurabili". Abbiamo così realizzato un oggetto in grado di accettare un set molto ampio di parametri esterni, così da avere modo di poter configurare il BlockSize, il Cipher mode, l'hash e il salt da utilizzare per la password (e relativo algoritmo), il numero di password hash iterations, l'Initialization Vector (IV), la lunghezza della chiave ovvero del KeyLength (nel caso in cui non vogliamo determinarla dinamicamente in base al bit-length della password utilizzata), il Salt, il Padding mode, e così via.
Il risultato dei nostri sforzi ha preso il nome di AESCrypt ed è al momento disponibile su GitHub su licenza Apache License 2.0, in attesa di avere il tempo e la voglia di pubblicarlo su NuGet. L'utilizzo è estremamente semplice e molto simile agli altri pacchetti AES disponibili, prevedendo un costruttore minimale - valido in tutti i casi in cui non abbiamo bisogno di configurare l'algoritmo di encryption in modo particolare - e un costruttore più avanzato che prevede la presenza di un oggetto di configurazione specifico contenente tutte le opzioni e impostazioni avanzate.
Esempi di uso
Di seguito vengono forniti alcuni casi di utilizzo comune, attraverso l'utilizzo dei metodi encrypt e decrypt in un tipico scenario applicativo:
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// text to encrypt var text = "Hello world!"; // passPhrase (32 bit length for AES256) var passPhrase = "12345678901234567890123456789012"; // Initialization Vector (16 bit length) var iv = "1234567890123456"; // Encrypt & Decrypt (with standard settings) var encryptedText = new AESCrypt(passPhrase, iv).Encrypt(); var sourceText = new AESCrypt(passPhrase, iv).Decrypt(encryptedText); // Encrypt & Decrypt (with advanced settings) var opts = new AESCryptOptions() { PasswordHash = AESPasswordHash.SHA1, PasswordHashIterations = 2, PasswordHashSalt = "23$9uBsDjf8", PaddingMode = PaddingMode.Zeroes, MinSaltLength = 4, MaxSaltLength = 8 }; var encryptedText = new AESCrypt(passPhrase, iv, opts).Encrypt(); var sourceText = new AESCrypt(passPhrase, iv, opts).Decrypt(encryptedText); |
Come è possibile vedere, possiamo utilizzare il costruttore semplice - con passPhrase e (opzionalmente) Initialization Vector - oppure il costruttore avanzato, al quale passare un oggetto AESCryptOptions opportunamente configurato.
Codice Sorgente
Il progetto AESCrypt è distribuito su licenza Apache License 2.0 ed è disponibile su GitHub: il nostro consiglio è di scaricarlo direttamente da lì, così da essere sicuri di prendere la versione più recente ed aggiornata.
Nei paragrafi seguenti presenteremo in dettaglio il funzionamento della libreria e pubblicheremo il codice sorgente completo di tutte le classi, corredato delle opportune spiegazioni e aggiornato alla data odierna: 13 luglio 2018.
La libreria si compone di tre classi:
- AESCrypt - il motore di encryption vero e proprio, contenente i metodi Encrypt e Decrypt e le relative implementazioni: queste ultime sono state realizzate facendo uso delle classi AesManaged e AESCryptOptions disponibili nel namespace System.Security.Cryptography di ASP.NET.
- AESCryptOptions - una classe POCO contenente le opzioni di encrypt/decrypt AES, preimpostate con le impostazioni predefinite più comuni.
- AESPasswordHash - un semplice ENUM contenente le diverse possibilità di password hashing - SHA1, MD5 or None.
AESCrypt.cs
Iniziamo con la classe principale, ovvero AESCrypt (file AESCrypt.cs):
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///////////////////////////////////////////////////////////////////////////////////////////////////// // AESCrypt - Symmetric key encryption and decryption using AES/Rijndael algorythm (128, 192 and 256) // https://www.ryadel.com/ , 2016 ///////////////////////////////////////////////////////////////////////////////////////////////////// using System; using System.IO; using System.Text; using System.Security.Cryptography; using System.ComponentModel; namespace Ryadel.Components.Security { /// <summary> /// This class uses a symmetric key algorithm (AES) to encrypt and decrypt data. As long as it is initialized with the same constructor /// parameters, the class will use the same key. Before performing encryption, the class can prepend random bytes to plain text and generate different /// encrypted values from the same plain text, encryption key, initialization vector, and other parameters. This class is thread-safe. /// </summary> public class AESCrypt { #region Private members // These members will be used to perform encryption and decryption. private ICryptoTransform encryptor = null; private ICryptoTransform decryptor = null; private AESCryptOptions Options = null; #endregion #region Constructors /// <summary> /// Use this constructor to perform encryption/decryption with the following options: /// - 128/192/256-bit key (depending on passPhrase length in bits) /// - SHA-1 password hashing algorithm with 4-to-8 byte long password hash salt and 1 password iteration /// - hashing without salt /// - no initialization vector /// - electronic codebook (ECB) mode /// </summary> /// <param name="passPhrase"> /// Passphrase (in string format) from which a pseudo-random password will be derived. The derived password will be used to generate the encryption key. /// </param> /// <remarks> /// This constructor is NOT recommended because it does not use initialization vector and uses the ECB cipher mode, which is less secure than the CBC mode. /// </remarks> public AESCrypt(string passPhrase) : this(passPhrase, null) { } /// <summary> /// Use this constructor to perform encryption/decryption with the following options: /// - 128/192/256-bit key (depending on passPhrase length in bits) /// - SHA-1 password hashing algorithm with 4-to-8 byte long password hash salt and 1 password iteration /// - hashing without salt /// - cipher block chaining (CBC) mode /// </summary> /// <param name="passPhrase"> /// Passphrase (in string format) from which a pseudo-random password will be derived. The derived password will be used to generate the encryption key. /// </param> /// <param name="initVector"> /// Initialization vector (IV). This value is required to encrypt the first block of plaintext data. IV must be exactly 16 ASCII characters long. /// </param> public AESCrypt(string passPhrase, string initVector) : this(passPhrase, initVector, new AESCryptOptions()) { } /// <summary> /// Use this constructor to perform encryption/decryption with custom options. /// See AESCryptOptions documentation for details. /// </summary> /// <param name="passPhrase"> /// Passphrase (in string format) from which a pseudo-random password will be derived. The derived password will be used to generate the encryption key. /// </param> /// <param name="initVector"> /// Initialization vector (IV). This value is required to encrypt the first block of plaintext data. IV must be exactly 16 ASCII characters long. /// </param> /// <param name="options"> /// A set of customized (or default) options to use for the encryption/decryption: see AESCryptOptions documentation for details. /// </param> public AESCrypt(string passPhrase, string initVector, AESCryptOptions options) { // store the options object locally. this.Options = options; // Checks for the correct (or null) size of cryptographic key. if (Options.FixedKeySize.HasValue && Options.FixedKeySize != 128 && Options.FixedKeySize != 192 && Options.FixedKeySize != 256) throw new NotSupportedException("ERROR: options.FixedKeySize must be NULL (for auto-detect) or have a value of 128, 192 or 256"); // Initialization vector converted to a byte array. byte[] initVectorBytes = null; // Salt used for password hashing (to generate the key, not during // encryption) converted to a byte array. byte[] saltValueBytes = null; // Get bytes of initialization vector. if (initVector == null) initVectorBytes = new byte[0]; else initVectorBytes = Encoding.UTF8.GetBytes(initVector); // Gets the KeySize int keySize = (Options.FixedKeySize.HasValue) ? Options.FixedKeySize.Value : GetAESKeySize(passPhrase); // Get bytes of password (hashing it or not) byte[] keyBytes = null; if (Options.PasswordHash == AESPasswordHash.None) { // Convert passPhrase to a byte array keyBytes = System.Text.Encoding.UTF8.GetBytes(passPhrase); } else { // Get bytes of password hash salt if (Options.PasswordHashSalt == null) saltValueBytes = new byte[0]; else saltValueBytes = Encoding.UTF8.GetBytes(options.PasswordHashSalt); // Generate password, which will be used to derive the key. PasswordDeriveBytes password = new PasswordDeriveBytes( passPhrase, saltValueBytes, Options.PasswordHash.ToString().ToUpper().Replace("-", ""), Options.PasswordHashIterations); // Convert key to a byte array adjusting the size from bits to bytes. keyBytes = password.GetBytes(keySize / 8); } // Initialize AES key object. AesManaged symmetricKey = new AesManaged(); // Sets the padding mode symmetricKey.Padding = Options.PaddingMode; // Use the unsafe ECB cypher mode (not recommended) if no IV has been provided, otherwise use the more secure CBC mode. symmetricKey.Mode = (initVectorBytes.Length == 0) ? CipherMode.ECB : CipherMode.CBC; // Create the encryptor and decryptor objects, which we will use for cryptographic operations. encryptor = symmetricKey.CreateEncryptor(keyBytes, initVectorBytes); decryptor = symmetricKey.CreateDecryptor(keyBytes, initVectorBytes); } #endregion #region Encryption routines /// <summary> /// Encrypts a string value generating a base64-encoded string. /// </summary> /// <param name="plainText"> /// Plain text string to be encrypted. /// </param> /// <returns> /// Cipher text formatted as a base64-encoded string. /// </returns> public string Encrypt(string plainText) { return Encrypt(Encoding.UTF8.GetBytes(plainText)); } /// <summary> /// Encrypts a byte array generating a base64-encoded string. /// </summary> /// <param name="plainTextBytes"> /// Plain text bytes to be encrypted. /// </param> /// <returns> /// Cipher text formatted as a base64-encoded string. /// </returns> public string Encrypt(byte[] plainTextBytes) { return Convert.ToBase64String(EncryptToBytes(plainTextBytes)); } /// <summary> /// Encrypts a string value generating a byte array of cipher text. /// </summary> /// <param name="plainText"> /// Plain text string to be encrypted. /// </param> /// <returns> /// Cipher text formatted as a byte array. /// </returns> public byte[] EncryptToBytes(string plainText) { return EncryptToBytes(Encoding.UTF8.GetBytes(plainText)); } /// <summary> /// Encrypts a byte array generating a byte array of cipher text. /// </summary> /// <param name="plainTextBytes"> /// Plain text bytes to be encrypted. /// </param> /// <returns> /// Cipher text formatted as a byte array. /// </returns> public byte[] EncryptToBytes(byte[] plainTextBytes) { // Add salt at the beginning of the plain text bytes (if needed). byte[] plainTextBytesWithSalt = (UseSalt()) ? AddSalt(plainTextBytes) : plainTextBytes; byte[] cipherTextBytes = null; // Let's make cryptographic operations thread-safe. lock (this) { // Encryption will be performed using memory stream. using (MemoryStream memoryStream = new MemoryStream()) { // To perform encryption, we must use the Write mode. using (CryptoStream cryptoStream = new CryptoStream( memoryStream, encryptor, CryptoStreamMode.Write)) { // Start encrypting data. cryptoStream.Write(plainTextBytesWithSalt, 0, plainTextBytesWithSalt.Length); // Finish the encryption operation. cryptoStream.FlushFinalBlock(); // Move encrypted data from memory into a byte array. cipherTextBytes = memoryStream.ToArray(); cryptoStream.Close(); } memoryStream.Close(); } // Return encrypted data. return cipherTextBytes; } } #endregion #region Decryption routines /// <summary> /// Decrypts a base64-encoded cipher text value generating a string result. /// </summary> /// <param name="cipherText"> /// Base64-encoded cipher text string to be decrypted. /// </param> /// <returns> /// Decrypted string value. /// </returns> public string Decrypt(string cipherText) { return Decrypt(Convert.FromBase64String(cipherText)); } /// <summary> /// Decrypts a byte array containing cipher text value and generates a /// string result. /// </summary> /// <param name="cipherTextBytes"> /// Byte array containing encrypted data. /// </param> /// <returns> /// Decrypted string value. /// </returns> public string Decrypt(byte[] cipherTextBytes) { return Encoding.UTF8.GetString(DecryptToBytes(cipherTextBytes)); } /// <summary> /// Decrypts a base64-encoded cipher text value and generates a byte array /// of plain text data. /// </summary> /// <param name="cipherText"> /// Base64-encoded cipher text string to be decrypted. /// </param> /// <returns> /// Byte array containing decrypted value. /// </returns> public byte[] DecryptToBytes(string cipherText) { return DecryptToBytes(Convert.FromBase64String(cipherText)); } /// <summary> /// Decrypts a base64-encoded cipher text value and generates a byte array /// of plain text data. /// </summary> /// <param name="cipherTextBytes"> /// Byte array containing encrypted data. /// </param> /// <returns> /// Byte array containing decrypted value. /// </returns> public byte[] DecryptToBytes(byte[] cipherTextBytes) { byte[] decryptedBytes = null; byte[] plainTextBytes = null; int decryptedByteCount = 0; int saltLen = 0; // Since we do not know how big decrypted value will be, use the same // size as cipher text. Cipher text is always longer than plain text // (in block cipher encryption), so we will just use the number of // decrypted data byte after we know how big it is. decryptedBytes = new byte[cipherTextBytes.Length]; // Let's make cryptographic operations thread-safe. lock (this) { using (MemoryStream memoryStream = new MemoryStream(cipherTextBytes)) { // To perform decryption, we must use the Read mode. using (CryptoStream cryptoStream = new CryptoStream( memoryStream, decryptor, CryptoStreamMode.Read)) { // Decrypting data and get the count of plain text bytes. decryptedByteCount = cryptoStream.Read(decryptedBytes, 0, decryptedBytes.Length); cryptoStream.Close(); } memoryStream.Close(); } } // If we are using salt, get its length from the first 4 bytes of plain text data. if (UseSalt()) { saltLen = (decryptedBytes[0] & 0x03) | (decryptedBytes[1] & 0x0c) | (decryptedBytes[2] & 0x30) | (decryptedBytes[3] & 0xc0); } // Allocate the byte array to hold the original plain text (without salt). plainTextBytes = new byte[decryptedByteCount - saltLen]; // Copy original plain text discarding the salt value if needed. Array.Copy(decryptedBytes, saltLen, plainTextBytes, 0, decryptedByteCount - saltLen); // Return original plain text value. return plainTextBytes; } #endregion #region Helper functions /// <summary> /// Gets the KeySize by the password length in bytes. /// </summary> /// <param name="p"></param> /// <returns></returns> public static int GetAESKeySize(string passPhrase) { switch (passPhrase.Length) { case 16: return 128; case 24: return 192; case 32: return 256; default: throw new NotSupportedException("ERROR: AES Password must be of 16, 24 or 32 bits length!"); } } /// <summary> /// Checks if salt must be used or not for the encryption/decryption. /// </summary> /// <returns></returns> private bool UseSalt() { // Use salt if the max salt value is greater than 0 and equal or greater than min salt length. return (Options.MaxSaltLength > 0 && Options.MaxSaltLength >= Options.MinSaltLength); } /// <summary> /// Adds an array of randomly generated bytes at the beginning of the /// array holding original plain text value. /// </summary> /// <param name="plainTextBytes"> /// Byte array containing original plain text value. /// </param> /// <returns> /// Either original array of plain text bytes (if salt is not used) or a /// modified array containing a randomly generated salt added at the /// beginning of the plain text bytes. /// </returns> private byte[] AddSalt(byte[] plainTextBytes) { // Additional check if (!UseSalt()) return plainTextBytes; // Generate the salt. byte[] saltBytes = GenerateSalt(Options.MinSaltLength, Options.MaxSaltLength); // Allocate array which will hold salt and plain text bytes. byte[] plainTextBytesWithSalt = new byte[plainTextBytes.Length + saltBytes.Length]; // First, copy salt bytes. Array.Copy(saltBytes, plainTextBytesWithSalt, saltBytes.Length); // Append plain text bytes to the salt value. Array.Copy(plainTextBytes, 0, plainTextBytesWithSalt, saltBytes.Length, plainTextBytes.Length); return plainTextBytesWithSalt; } /// <summary> /// Generates an array holding cryptographically strong bytes. /// </summary> /// <returns> /// Array of randomly generated bytes. /// </returns> /// <remarks> /// Salt size will be defined at random or exactly as specified by the /// minSlatLen and maxSaltLen parameters passed to the object constructor. /// The first four bytes of the salt array will contain the salt length /// split into four two-bit pieces. /// </remarks> private byte[] GenerateSalt(int minSaltLen, int maxSaltLen) { // We don't have the length, yet. int saltLen = 0; // If min and max salt values are the same, it should not be random. if (minSaltLen == maxSaltLen) saltLen = minSaltLen; // Use random number generator to calculate salt length. else saltLen = GenerateRandomNumber(minSaltLen, maxSaltLen); // Allocate byte array to hold our salt. byte[] salt = new byte[saltLen]; // Populate salt with cryptographically strong bytes. RNGCryptoServiceProvider rng = new RNGCryptoServiceProvider(); rng.GetNonZeroBytes(salt); // Split salt length (always one byte) into four two-bit pieces and // store these pieces in the first four bytes of the salt array. salt[0] = (byte)((salt[0] & 0xfc) | (saltLen & 0x03)); salt[1] = (byte)((salt[1] & 0xf3) | (saltLen & 0x0c)); salt[2] = (byte)((salt[2] & 0xcf) | (saltLen & 0x30)); salt[3] = (byte)((salt[3] & 0x3f) | (saltLen & 0xc0)); return salt; } /// <summary> /// Generates random integer. /// </summary> /// <param name="minValue"> /// Min value (inclusive). /// </param> /// <param name="maxValue"> /// Max value (inclusive). /// </param> /// <returns> /// Random integer value between the min and max values (inclusive). /// </returns> /// <remarks> /// This methods overcomes the limitations of .NET Framework's Random /// class, which - when initialized multiple times within a very short /// period of time - can generate the same "random" number. /// </remarks> private int GenerateRandomNumber(int minValue, int maxValue) { // We will make up an integer seed from 4 bytes of this array. byte[] randomBytes = new byte[4]; // Generate 4 random bytes. RNGCryptoServiceProvider rng = new RNGCryptoServiceProvider(); rng.GetBytes(randomBytes); // Convert four random bytes into a positive integer value. int seed = ((randomBytes[0] & 0x7f) << 24) | (randomBytes[1] << 16) | (randomBytes[2] << 8) | (randomBytes[3]); // Now, this looks more like real randomization. Random random = new Random(seed); // Calculate a random number. return random.Next(minValue, maxValue + 1); } #endregion } } |
AESCryptOptions.cs
Questa è la classe POCO AESCryptOptions (file AESCryptOptions.cs):
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///////////////////////////////////////////////////////////////////////////////////////////////////// // AESCrypt - Symmetric key encryption and decryption using AES/Rijndael algorythm (128, 192 and 256) // https://www.ryadel.com/ , 2016 ///////////////////////////////////////////////////////////////////////////////////////////////////// using System.Security.Cryptography; namespace Ryadel.Components.Security { public class AESCryptOptions { #region Private members // Do not allow salt to be longer than 255 bytes, because we have only // 1 byte to store its length. private static int MAX_ALLOWED_SALT_LEN = 255; // Do not allow salt to be smaller than 4 bytes, because we use the first // 4 bytes of salt to store its length. private static int MIN_ALLOWED_SALT_LEN = 4; // Random salt value will be between 4 and 8 bytes long. private static int DEFAULT_MIN_SALT_LEN = MIN_ALLOWED_SALT_LEN; private static int DEFAULT_MAX_SALT_LEN = 8; // These members will be used to perform encryption and decryption. private ICryptoTransform encryptor = null; private ICryptoTransform decryptor = null; #endregion #region Constructor public AESCryptOptions() { PasswordHash = AESPasswordHash.SHA1; PasswordHashIterations = 1; MinSaltLength = 0; MaxSaltLength = 0; FixedKeySize = null; PaddingMode = PaddingMode.PKCS7; } #endregion #region Properties /// <summary> /// Key Size: this is typically 128, 192 or 256, depending on the password length in bit (16, 24 or 32 respectively). /// Default is NULL, meaning that it will be calculated on-the-fly using the password bit length. /// </summary> public int? FixedKeySize { get; set; } /// <summary> /// Password hashing mode: None, MD5 or SHA1. /// SHA1 is the recommended mode for most scenarios. /// </summary> public AESPasswordHash PasswordHash { get; set; } /// <summary> /// Password iterations - not used when [PasswordHash] is set to [AESPasswordHash.None] /// </summary> public int PasswordHashIterations { get; set; } /// <summary> /// Minimum Salt Length: must be equal or smaller than MaxSaltLength. /// Default is 0. /// </summary> public int MinSaltLength { get; set; } /// <summary> /// Maximum Salt Length: must be equal or greater than MinSaltLength. /// Default is 0, meaning that no salt will be used. /// </summary> public int MaxSaltLength { get; set; } /// <summary> /// Salt value used for password hashing during key generation. /// NOTE: This is not the same as the salt we will use during encryption. /// This parameter can be any string (set it to NULL for no password hash salt): default is NULL. /// </summary> public string PasswordHashSalt { get; set; } /// <summary> /// Sets the Padding Mode (default is PaddingMode.PKCS7) /// </summary> public PaddingMode PaddingMode { get; set; } #endregion } } |
AESPasswordHash.cs
Infine, questo è l'enum AESPasswordHash (file AESPasswordHash.cs):
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///////////////////////////////////////////////////////////////////////////////////////////////////// // AESCrypt - Symmetric key encryption and decryption using AES/Rijndael algorythm (128, 192 and 256) // https://www.ryadel.com/ , 2016 ///////////////////////////////////////////////////////////////////////////////////////////////////// namespace Ryadel.Components.Security { /// <summary> /// AES Password Hash: set "None" for no hashing. /// </summary> public enum AESPasswordHash : int { None = 0, MD5 = 1, SHA1 = 2 } } |
Tutte le classi di cui sopra sono provviste di una documentazione inline che spiega le funzionalità principali di ciascun metodo: non dovrebbe quindi essere difficile orientarsi per uno sviluppatore, a prescindere dal livello di esperienza... è sufficiente seguire le indicazioni fornite dall'Intellisense.
Anche per questa volta è tutto: ci auguriamo che questa libreria possa venire incontro alle esigenze di qualche altro sviluppatore ASP.NET che si troverà con l'esigenza di dover implementare l'algoritmo di encryption AES all'interno del proprio progetto!
