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(VB.NET) Generate Encryption Key

Discusses symmetric encryption key generation techniques for block encryption algorithms such as AES, Blowfish, and Twofish, or for other algorithms such as ChaCha20.

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'  Symmetric encryption algorithms are such that the encryptor and decryptor
'  share a pre-known secret key.  This could be a "single-use" key that is
'  derived from a secure key exchange algorithm using RSA, ECC, or Diffie-Hellman,
'  or it could be a password known to both sides, or
'  it could simply be the binary bytes of the secret key known in advance on both
'  sides.

'  A secret key has no structure.  It's nothing more than N bytes of data.
'  It should typically be random data, or bytes that resemble random data such
'  as the hash of a password.

'  The number of bytes in the secret key defines the bit-strength of an encryption
'  algorithm.  For example, AES with a 32-byte key is 256-bit AES.  Most algorithms
'  define restrictions on key sizes.  For example, AES has 3 choices: 128-bit, 192-bit,
'  or 256-bit.  In the ChaCha20 algorithm, the key size must always be 256-bits (32-bytes).

'  Both sides (encryptor and decryptor) must be in possession of the same secret key
'  in order to communicate.   Whichever side generates the key, it must somehow
'  deliver the key to the other side beforehand.  Key exchange algorithms, such as RSA, ECC,
'  and Diffie-Hellman define secure ways of exchanging symmetric encryption keys.
'  They do so using asymmetric encryption algorithms (public/private keys).  It is not
'  required to use a key exchange algorithm to achieve the goal of having both sides
'  in possession of the same secret key.  A long-living secret key could be exchanged
'  via any secure out-of-band means.  For example, exchanging the information over a secure
'  TLS (HTTPS) or SSH connection...

'  This example assumes the Chilkat API to have been previously unlocked.
'  See Global Unlock Sample for sample code.

Dim success As Boolean

Dim crypt As New Chilkat.Crypt2
crypt.CryptAlgorithm = "aes"
crypt.KeyLength = 256

'  Generate a 32-byte random secret key,
'  and use it in the crypt object.
Dim prng As New Chilkat.Prng
Dim secretKeyHex As String = prng.GenRandom(32,"hex")
'  It is important that the number of bytes in the secret key
'  matches the value specified in the KeyLength property (above).
crypt.SetEncodedKey(secretKeyHex,"hex")
Console.WriteLine("randomly generated key: " & secretKeyHex)

'  Alternatively, a password could be hashed using a hash algorithm
'  the results in the desired key length.  Our desired key length
'  in this case is 32 bytes, so we wouldn't want MD5 (16 bytes),
'  nor would we want to use SHA-1 (20 bytes).  SHA256 would be the
'  hash of choice because it results in 32-bytes of random-looking
'  key material.
crypt.HashAlgorithm = "SHA256"
crypt.EncodingMode = "hex"
secretKeyHex = crypt.HashStringENC("mypassword")
crypt.SetEncodedKey(secretKeyHex,"hex")
Console.WriteLine("password-based key: " & secretKeyHex)

 

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