Crypto

Provides basic RSA, blowfish and CSPRNG functions. Supports OAEP and PKCS v1.5 padding.

Examples

Generate a 1024 bit RSA key pair:

set K	[crypto::rsa::RSAKG 1024 0x10001]

Sign a string using RSA with OAEP and SHA256:

set signature	[crypto::rsa::RSAES-OAEP-Sign \
	[dict get $K n] \
	[dict get $K d] \
	[encoding convertto utf-8 "This is the data I want to sign"] \
	{} \
	$::crypto::rsa::sha256 \
	$::crypto::rsa::MGF]

Generate a blowfish session key and encrypt it with an RSA public key:

set key		[crypto::blowfish::csprng 56]
set e_key	[crypto::rsa::RSAES-OAEP-Encrypt \
	[dict get $K n] \
	[dict get $K e] \
	$key \
	{} \
	$crypto::rsa::sha256 \
	$crypto::rsa::MGF]

Decrypt a session key with an RSA private key:

set key		[crypto::rsa::RSAES-OAEP-Decrypt \
	[list \
		[dict get $K p] \
		[dict get $K q] \
		[dict get $K dP] \
		[dict get $K dQ] \
		[dict get $K qInv] \
	] \
	$e_key \
	{}
	$crypto::rsa::sha265 \
	$crypto::rsa::MGF]

Encrypt and decrypt a message with blowfish in CBC (Cipher Block Chaining) mode:

# Client
set plaintext    "hello, world"
set key          [crypto::blowfish::csprng 56]
set ks           [crypto::blowfish::init_key $key]
set iv           [crypto::blowfish 8]
set ciphertext   [crypto::blowfish::encrypt_cbc $ks [encoding convertto utf-8 $plaintext] $iv
set e_msg        $iv$ciphertext
# send $e_msg to server

# Server
# assumes $key from client, transferred security using RSA as in the above examples
set ks           [crypto::blowfish::init_key $key]
set iv           [string range $e_msg 0 7]
set cipertext    [string range $e_msg 8 end]
set plaintext    [encoding convertfrom utf-8 [crypto::blowfish::decrypt_cbc $ks $ciphertext $iv]]
# $plaintext is "hello, world"

Building

This uses tbuild to build the .tm. You very likely don't have tbuild, so just use the pre-built .tm included in the repo.

Security

While I have been careful to adhere to the implementation guidelines as closely as possible, no cryptographic audit has been performed on this code and I make no warrenties as to its correctness or security. You are encouraged to examine the code yourself or get a qualified cryptographer to audit this code before using it in an application with specific security requirements.

In particular it should be noted that key privacy is poor - the limitations of working in a scripting language means that the keys could be leaked through freed memory, so this code should not be used in any situation where an attacker could have access to system memory. Certain timing attacks are also probably made more feasible because the script runs more slowly than native code, magnifying the effects of taking different branches in the code.

License

This package is licensed under the same terms as the Tcl core.