(Tcl) RSA Decrypt using Private Key on Smartcard or USB Token via Apple Keychain

See more Apple Keychain Examples

RSA decryption using a certificate's private key located on a hardware token or smartcard via the Apple Keychain.

Note: This example requires Chilkat v10.1.2 or greater.

Chilkat Tcl Extension Downloads Chilkat Tcl Extension Downloads

load ./chilkat.dll

# Beforehand, we generated a 256-bit AES key, RSA encrypted, and saved to a file as in this example:
# Generate a Random 256-bit AES Key and RSA Encrypt

# The RSA public key used to encrypt in the above example was obtained from the Apple Keychain
# like this:
# Export a Public Key from USB Token or Smartcard using the Apple Keychain

# This example will load the encrypted data and will RSA decrypt using the 
# private key of a certificate on a USB token (or smart card) via the Keychain.
# You can list the Keychain certificates on hardware tokens using the following example:
# Apple Keychain - List Certs on Smartcards and USB Tokens

# Get the RSA encrypted data to be decrypted.
set bd [new_CkBinData]

# In all Chilkat methods expecting a path, you can pass either absolute or relative paths.
set success [CkBinData_LoadFile $bd "rsaEncrypted/myAes.key"]
if {$success == 0} then {
    puts "Failed to load the encrypted AES key."
    delete_CkBinData $bd
    exit
}

# Load the certificate having the private key from the Apple Keychain
# On MacOS and iOS, the LoadByCommonName function will search the Apple Keychain for the matching certificate.
set cert [new_CkCert]

# To potentially prevent the PIN dialog from being displayed,
# we'll need to provide the USB token (or smart card) PIN
# Note: It might not be possible to prevent the PIN dialog from being displayed
# 
CkCert_put_SmartCardPin $cert "123456"

set success [CkCert_LoadByCommonName $cert "Test 2048 bit RSA"]
if {$success == 0} then {
    puts [CkCert_lastErrorText $cert]
    delete_CkBinData $bd
    delete_CkCert $cert
    exit
}

set rsa [new_CkRsa]

# Specify we wish to use the certificate's private key for decryption.
set success [CkRsa_SetX509Cert $rsa $cert 1]
if {$success == 0} then {
    puts [CkRsa_lastErrorText $rsa]
    delete_CkBinData $bd
    delete_CkCert $cert
    delete_CkRsa $rsa
    exit
}

# RSA Decrypt
CkRsa_put_VerboseLogging $rsa 1
set success [CkRsa_DecryptBd $rsa $bd 1]
if {$success == 0} then {
    puts [CkRsa_lastErrorText $rsa]
    delete_CkBinData $bd
    delete_CkCert $cert
    delete_CkRsa $rsa
    exit
}

# The contents of bd are now decrypted.
puts "Num bytes after decryption: [CkBinData_get_NumBytes $bd]"

# Some additional notes:
# 
# If using a Yubikey token, the certificate must be installed in the Key Management slot.
# The Digital Signature slot is for RSA keys to be used for signing, 
# and the Key Management slot is for RSA keys to be used for decrypting.
# 

# If you try to use the RSA key from the Digital Signature slot, you'll get an error such as this:

# The operation couldn't be completed. 
# (OSStatus error -50 - algid:encrypt:RSA:PKCS1: algorithm not supported by the key 
# <SecKeyRef:('com.apple.pivtoken:AF7172EB60DDCBF1D28459AE24398E11') 0x600001ecca90>)

delete_CkBinData $bd
delete_CkCert $cert
delete_CkRsa $rsa