(Tcl) JWE using AES Key Wrap and AES_128_CBC_HMAC_SHA_256

This example duplicates the example A.3 in RFC 7516 for JSON Web Encryption (JWE).

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

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load ./chilkat.dll

# 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: {"alg":"A128KW","enc":"A128CBC-HS256"}
set jweProtHdr [new_CkJsonObject]

CkJsonObject_AppendString $jweProtHdr "alg" "A128KW"
CkJsonObject_AppendString $jweProtHdr "enc" "A128CBC-HS256"
CkJwe_SetProtectedHeader $jwe $jweProtHdr

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

# The example A.3 in RFC 7516 uses the following 128-bit AES key,
# specified in JWK (JSON Web Key) format:
#      {"kty":"oct",
#       "k":"GawgguFyGrWKav7AX4VKUg"
#      }
# This is just a way of saying: The key type ("kty") is 
# a bunch of octets ("k") in base64url encoding.
# We can simply set the AES wrapping key like this:
set aesWrappingKey "GawgguFyGrWKav7AX4VKUg"
CkJwe_SetWrappingKey $jwe 0 $aesWrappingKey "base64url"

# 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 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_CkJwe $jwe2
    exit
}

# Set the AES wrap key.
CkJwe_SetWrappingKey $jwe2 0 $aesWrappingKey "base64url"

# 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"

# ---------------------------------------------------------------------------------
# It should also be possible to decrypt the JWE as shown in RFC 7516, Appendix A.3.7
# because it was produced using the same AES Wrap key.

set sbJwe [new_CkStringBuilder]

CkStringBuilder_Append $sbJwe "eyJhbGciOiJBMTI4S1ciLCJlbmMiOiJBMTI4Q0JDLUhTMjU2In0."
CkStringBuilder_Append $sbJwe "6KB707dM9YTIgHtLvtgWQ8mKwboJW3of9locizkDTHzBC2IlrT1oOQ."
CkStringBuilder_Append $sbJwe "AxY8DCtDaGlsbGljb3RoZQ."
CkStringBuilder_Append $sbJwe "KDlTtXchhZTGufMYmOYGS4HffxPSUrfmqCHXaI9wOGY."
CkStringBuilder_Append $sbJwe "U0m_YmjN04DJvceFICbCVQ"

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

CkJwe_SetWrappingKey $jwe2 0 $aesWrappingKey "base64url"

# 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
    delete_CkStringBuilder $sbJwe
    exit
}

puts "$originalPlaintext"

delete_CkJwe $jwe
delete_CkJsonObject $jweProtHdr
delete_CkJwe $jwe2
delete_CkStringBuilder $sbJwe