Tcl

JWE using "dir" Direct use of Shared Symmetric Key

See more JSON Web Encryption (JWE) Examples

Demonstrates how to create a JWE using the "dir" alg -- which is to directly use a shared symmetric key.

Note: This example requires Chilkat v9.5.0.66 or greater.

Tcl

load ./chilkat.dll

set success 0

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

# Note: This example requires Chilkat v9.5.0.66 or greater.

set plaintext "Live long and prosper."

set jwe [new_CkJwe]

# First build the JWE Protected Header..
set jweProtHdr [new_CkJsonObject]

CkJsonObject_AppendString $jweProtHdr "alg" "dir"
CkJsonObject_AppendString $jweProtHdr "enc" "A128GCM"

# Don't forget to actually provide the protected header to the JWE object:
CkJwe_SetProtectedHeader $jwe $jweProtHdr

# The JWE is to use 128-bit AES GCM encryption as specified by the "enc" parameter.
# Given that the "alg" = "dir", we are to directly specify the AES GCM key.
# (It is assumed that the decrypting side also has knowledge of the direct key to be used..)

# Our key will be these 16 hex bytes: 000102030405060708090A0B0C0D0E0F

# The SetWrappingKey method is also used for "dir" direct keys.
# However, if there are multiple recipients, they must all share the same CEK (Content Encryption Key),
# which is specified by calling SetWrappingKey with an index of 0.

set recipientIndex 0
CkJwe_SetWrappingKey $jwe $recipientIndex "000102030405060708090A0B0C0D0E0F" "hex"

# Encrypt and return the JWE:
set strJwe [CkJwe_encrypt $jwe $plaintext "utf-8"]
if {[CkJwe_get_LastMethodSuccess $jwe] != 1} then {
    puts [CkJwe_lastErrorText $jwe]
    delete_CkJwe $jwe
    delete_CkJsonObject $jweProtHdr
    exit
}

# Show the JWE we just created:
puts "$strJwe"

# Decrypt the JWE.
set jwe2 [new_CkJwe]

set success [CkJwe_LoadJwe $jwe2 $strJwe]
if {$success != 1} then {
    puts [CkJwe_lastErrorText $jwe2]
    delete_CkJwe $jwe
    delete_CkJsonObject $jweProtHdr
    delete_CkJwe $jwe2
    exit
}

CkJwe_SetWrappingKey $jwe2 0 "000102030405060708090A0B0C0D0E0F" "hex"

# Decrypt.
set originalPlaintext [CkJwe_decrypt $jwe2 0 "utf-8"]
if {[CkJwe_get_LastMethodSuccess $jwe2] != 1} then {
    puts [CkJwe_lastErrorText $jwe2]
    delete_CkJwe $jwe
    delete_CkJsonObject $jweProtHdr
    delete_CkJwe $jwe2
    exit
}

puts "original text: "
puts "$originalPlaintext"

# Sample output:
# eyJhbGciOiJkaXIiLCJlbmMiOiJBMTI4R0NNIn0..20HX5Huc7f1nQC4pBUtiCQ.axFZIxtZy5j0ifJQUzGXLKIpsBuxJA.eBrOC-NrsreN6JeGuOPk1g
# original text: 
# Live long and prosper.

delete_CkJwe $jwe
delete_CkJsonObject $jweProtHdr
delete_CkJwe $jwe2