(Tcl) JWE using PBES2 Key Wrapping

Demonstrates how to create and decrypt a JWE that using PBES2 key wrapping.

This example demonstrates PBES2 with HMAC SHA-256 and A128KW wrapping. It is also possible to do the following by simply changing the "alg" parameter:

• PBES2 with HMAC SHA-384 and A192KW wrapping
• PBES2 with HMAC SHA-512 and A256KW wrapping

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..
set jweProtHdr [new_CkJsonObject]

CkJsonObject_AppendString $jweProtHdr "alg" "PBES2-HS256+A128KW"
CkJsonObject_AppendString $jweProtHdr "enc" "A128GCM"

# PBES2 requires two additional parameters:
# 1) A random salt parameter ("p2s") containing 8 or more bytes in base64url format.
# 2) An iteration count parameter ("p2c").  A minimum count of 1000 is recommended.
#    The iteration count is intended to make the PBES2 computation more expensive (time consuming)
#    to prevent brute-force attacks.
set prng [new_CkPrng]

CkJsonObject_AppendString $jweProtHdr "p2s" [CkPrng_genRandom $prng 16 "base64url"]
CkJsonObject_AppendString $jweProtHdr "p2c" "1000"

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

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

# Set the PBES2 password
set recipientIndex 0
CkJwe_SetPassword $jwe $recipientIndex "top secret"

# 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.
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 PBES2 password
CkJwe_SetPassword $jwe2 $recipientIndex "top secret"

# 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"

# Sample output:

# JWE Protected Header: {"alg":"PBES2-HS256+A128KW","enc":"A128GCM","p2s":"z39rTEfRy1T1Yn_D1mZRlg","p2c":"1000"}
# --
# eyJhbGciOiJQQkVTMi1IUzI1NitBMTI4S1ciLCJlbmMiOiJBMTI4R0NNIiwicDJzIjoiejM5clRFZlJ5MVQxWW5fRDFtWlJsZyIsInAyYyI6IjEwMDAifQ.koYt6PrFmYwcwdcT7ZcvXHA1d-Xez5h4.luGlbvEnZp-7IsBOj42Yhw.YMTcfLf8Qe4zazozGV2OAu3cUdQ8Kg.rWub47ESWkc6IqZJTvSTmg
# original text: 
# Live long and prosper.

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