Tcl

Charset Considerations when RSA Encrypting Strings

See more RSA Examples

When encrypting strings, character encoding can be an issue. Encryption algorithms operate on binary data. If for example, your string includes a character such as é, the bytes used to represent it depend on the character encoding. In an "iso" encoding such as iso-8859-1, or in a "windows" encoding, such as "windows-1252", the é is represented by a single byte. In Unicode however, whether it's utf-8 or ucs-2, the é is represented by 2 bytes. When encrypting strings, the RSA component will first convert the string to the character encoding indicated by the Charset property. When decrypting strings, the RSA component converts from the character encoding indicated by the Charset property to the application's expected charset. In VB6 for example, this would be Unicode. In C++, it's ANSI. In Java, it's utf-8. Tcl

load ./chilkat.dll

set success 0

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

set rsa [new_CkRsa]

# RSA public key in XML format:
set pubKeyXml "<RSAPublicKey><Modulus>of3im3mRgd2NLXIGoK6uYLg6jj0Ug2b42rnqa5Tbwz2ieFqMJqt+++x2oqLYGurlz49nt+7/785g3XYWqoka4u9c9zul6YubIjnBM72dQy7rEkEfbUxgjcxqXyjZFx+FpaxFUecLu688XEu+9UA42VKiCgcl+E7TrqnfeeYpNXc=</Modulus><Exponent>AQAB</Exponent></RSAPublicKey>"

set pubKey [new_CkPublicKey]

set success [CkPublicKey_LoadFromString $pubKey $pubKeyXml]
if {$success == 0} then {
    puts [CkPublicKey_lastErrorText $pubKey]
    delete_CkRsa $rsa
    delete_CkPublicKey $pubKey
    exit
}

set success [CkRsa_UsePublicKey $rsa $pubKey]
if {$success == 0} then {
    puts [CkRsa_lastErrorText $rsa]
    delete_CkRsa $rsa
    delete_CkPublicKey $pubKey
    exit
}

# Use the utf-8 character encoding.  When encrypting, the
# plain text is first converted to utf-8 bytes and then
# RSA encrypted.
CkRsa_put_Charset $rsa "utf-8"

# Encrypt a string and return the encrypted data base64-encoded:
CkRsa_put_EncodingMode $rsa "base64"

set plainText "éééé"

set usePrivateKey 0
set encryptedStr [CkRsa_encryptStringENC $rsa $plainText $usePrivateKey]
puts "$encryptedStr"

delete_CkRsa $rsa
delete_CkPublicKey $pubKey