Encrypting variable-length strings with a password Introduction This page shows how to encrypt a variable-length text string with a key derived from a text password. It uses AES-128, but could use any of the major encryption algorithms like Triple DES or Blowfish. All the necessary cryptographic functions are provided in the library. Vb6 Source Code Example• • • • • • • • • • Example Projects There are two example projects. • A VB.NET project that emphasises the steps involved in encryption and decryption using hex-encoding for clarity. • A VB6 project that shows three possible ways to create a key from a password and how the final ciphertext and initialization vector could be transmitted to the recipient in base64 format. In both cases, we wish to encrypt an ordinary text message using a password or pass phrase string and transmit the ciphertext to a recipient. We assume that the sender and recipient have already agreed on the secret password (which they've passed to each other using a separate, secure channel) and the other necessary parameters. These examples use AES-128 in Cipher Block Chaining (CBC) mode with PKCS#5 padding. Simple String Encryption and Decryption with Source Code. I'm using your code to encrypt a query string. I'm also using your code to encrypt and decrypt. Visual Basic 6: Code needed. 2003 and used by a VB6 program. The encryption routine code is in a. You need to transmit the ciphertext to the recipient as well as the Initialization Vector, Salt and Iteration Count used. In the most general case, the sender needs to transmit the following information: Ciphertext=. IterationCount=nnn In practice, you can be more succinct. We suggest that sender and recipient agree on these conventions beforehand: • The iteration count is always the same value (e.g. This saves having to transmit it each time. • The IV and salt will be the same value. This will be exactly 16 bytes (128 bits = the block size) for AES. There is no conflict in using the same value for both these purposes and it reduces the information you need to transmit. • The message will be transmitted in the form Base64Encode(IV|| ciphertext). https://makecareers182.weebly.com/blog/pro-cycling-manager-mac-free-download. Using base64 encoding makes transmission easy. The recipient just needs to decode and then separate out the first 16 bytes for the IV/salt. Alternatively use hexadecimal encoding. Obviously you can agree on and use many other variations of this. Just be consistent. Just click download title, then click download now button or copy download link to browser and wait certain amount of time (usually up to 30 seconds) for download to begin. Security considerations • Do not use ECB mode! There are several modes of operation for block ciphers: ECB (Electronic CodeBook), CBC (Cipher Block Chaining), CFB (Cipher FeedBack), OFB (Output FeedBack) and CTR (Counter). For further details, see []. In some packages, the default mode is ECB. It is not secure. Always use CBC (Cipher Block Chaining) mode. This requires you to provide a separate Initialization Vector (IV) which must be unique for every message you ever send using the same key. • A password is not a key! A password is a text string of variable length. Encryption algorithms require the key as a fixed-length bit-string. You must convert the password text string to a bit-string. Use the Password-Based Key Derivation Function algorithm known as PBKDF2 to do this. This method requires a random salt and an iteration count as well as the password text. For convenience, you can use the same random value for the salt as for the IV. Just make sure that the sender and recipient agree on this convention. • Ciphertext is not text! Ciphertext is a bit string that should not be stored in a 'string' type. Encode the ciphertext in hexadecimal or base64, which can be safely stored and transmitted as a string type. • Use a unique IV each time! Always create a fresh, randomly-generated IV/salt each and every time you encrypt a new message to send. Never give your users the opportunity to re-use an old one or avoid the automatic re-generation process. Algorithms Encryption Algorithm. Algorithm: Encryption with password using block cipher in CBC mode INPUT: • Plaintext inputText in text format. • A pre-agreed secret password in text format. • iterationCount, an integer > 1000. Star wars homeworld 2 download. Download Homeworld 2 • Windows Games @ The Iso Zone • The Ultimate Retro Gaming Resource. • Encryption algorithm (e.g. AES-128) with given keySize and blockSize. OUTPUT: • Initialization Vector iv in bit-string format. • cipherText in bit-string format. • Generate a random value of the same size as the block length of the encryption algorithm randVal = GenerateRandomValue(blockSize) • Set iv = randVal salt = randVal • Generate a key of the required size for the encryption algorithm key=KDF2(password, salt, iterationCount, keySize) • Convert the input text to `binary' format work = BitStringFromText(inputText). • Pad this to the next-highest multiple of the encryption block size work = Pad(work, blockSize). • Encrypt the working block in CBC mode using the key and IV ciphertext = EncryptCBC(work, key, iv) • Output iv and cipherText. Decryption Algorithm. Algorithm: Decryption with password using block cipher in CBC mode INPUT: • cipherText in bit-string format. • A pre-agreed secret password in text format.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |