Tcl

JWE using A256GCMKW

See more JSON Web Encryption (JWE) Examples

This example demonstrates creating a JCE with AES GCM key wrap. Tcl

load ./chilkat.dll

set success 0

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

set plaintext "My text to enrypt"

set jwe [new_CkJwe]

# First build the JWE Protected Header: 

#         {
#             "alg": "A256GCMKW",
#             "kid": "18ec08e1-bfa9-4d95-b205-2b4dd1d4321d",
#             "tag": "kfPduVQ3T3H6vnewt--ksw",
#             "iv": "KkYT0GX_2jHlfqN_",
#             "enc": "A128CBC-HS256"
#         }

set jweProtHdr [new_CkJsonObject]

CkJsonObject_AppendString $jweProtHdr "alg" "A256GCMKW"
# kid is optional
CkJsonObject_AppendString $jweProtHdr "kid" "18ec08e1-bfa9-4d95-b205-2b4dd1d4321d"
# tag is optional
CkJsonObject_AppendString $jweProtHdr "tag" "kfPduVQ3T3H6vnewt--ksw"
CkJsonObject_AppendString $jweProtHdr "enc" "A256GCM"
# the iv should be 16 random chars.
set prng [new_CkPrng]

CkJsonObject_AppendString $jweProtHdr "iv" [CkPrng_randomString $prng 16 1 1 1]
CkJwe_SetProtectedHeader $jwe $jweProtHdr

puts "JWE Protected Header: [CkJsonObject_emit $jweProtHdr]"
puts "--"

# Given that we have 256-bit AES, our key should be 32 bytes.
# The ascii string here is 32 bytes, therefore the 2nd arg is "ascii" to use these
# ascii chars directly as the key.
set aesWrappingKey "2baf4f730f5e4542b428593ef9cceb0e"
CkJwe_SetWrappingKey $jwe 0 $aesWrappingKey "ascii"

# 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
    delete_CkPrng $prng
    exit
}

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

# Decrypt the JWE that was just produced.
# 1) Load the JWE.
# 2) Set the AES wrapping key.
# 3) Decrypt.
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_CkPrng $prng
    delete_CkJwe $jwe2
    exit
}

# Set the AES wrap key.  Important to use "ascii"
CkJwe_SetWrappingKey $jwe2 0 $aesWrappingKey "ascii"

# 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_CkPrng $prng
    delete_CkJwe $jwe2
    exit
}

puts "original text: "
puts "$originalPlaintext"

delete_CkJwe $jwe
delete_CkJsonObject $jweProtHdr
delete_CkPrng $prng
delete_CkJwe $jwe2