(Tcl) JWE Using Flattened JWE JSON Serialization

This example duplicates the example A.5 in RFC 7516 for JSON Web Encryption (JWE).

This example demonstrates using the flattened JWE JSON Serialization syntax. This example demonstrates the capability for encrypting the plaintext to a single recipient in a flattened JSON structure.

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: {"enc":"A128CBC-HS256"}
set jweProtHdr [new_CkJsonObject]

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

# We have a single recipient that uses AES Key Wrap to encrypt the CEK.
# 
#      {"alg":"A128KW","kid":"7"}

set jweRecipientHdr [new_CkJsonObject]

CkJsonObject_AppendString $jweRecipientHdr "alg" "A128KW"
CkJsonObject_AppendString $jweRecipientHdr "kid" "7"
set recipientIndex 0
CkJwe_SetRecipientHeader $jwe $recipientIndex $jweRecipientHdr

# Set the Shared Unprotected Header:  {"jku":"https://server.example.com/keys.jwks"}
set jweUnprotHdr [new_CkJsonObject]

CkJsonObject_AppendString $jweUnprotHdr "jku" "https://server.example.com/keys.jwks"
CkJwe_SetUnprotectedHeader $jwe $jweUnprotHdr

# Set the AES key wrapping key.
set aesWrappingKey "GawgguFyGrWKav7AX4VKUg"
set recipientIndex 0
CkJwe_SetWrappingKey $jwe $recipientIndex $aesWrappingKey "base64url"

# OK.. everything has been specified.
# Now encrypt.  
# Indicate that we prefer the flattened JSON serialization.
CkJwe_put_PreferFlattened $jwe 1
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_CkJsonObject $jweRecipientHdr
    delete_CkJsonObject $jweUnprotHdr
    exit
}

# The JWE is produced in the most compact form possible (a single line).
# Let's load it into a JSON object and examine in a non-compact pretty-printed format:
set jsonTemp [new_CkJsonObject]

CkJsonObject_Load $jsonTemp $strJwe
CkJsonObject_put_EmitCompact $jsonTemp 0
puts [CkJsonObject_emit $jsonTemp]

# The JWE looks like this:
# (Note: Because of random values used in the encryption process, your encrypted results will be different.)

# 	{ 
# 	  "protected": "eyJlbmMiOiJBMTI4Q0JDLUhTMjU2In0",
# 	  "unprotected": { 
# 	    "jku": "https://server.example.com/keys.jwks"
# 	  },
# 	  "header": { 
# 	    "alg": "A128KW",
# 	    "kid": "7"
# 	  },
# 	  "encrypted_key": "FW7z9VxOvnF2ClicvUT4HTeqcdyh90C6qytfEFJsOb77FOwTfYrc3w",
# 	  "iv": "O6Ly5-eML3zTs-_fNX3D5Q",
# 	  "ciphertext": "Q8NLmeac9JhLh0CQPuG_7D9wVDb55eToCh0g5-FQ4M0",
# 	  "tag": "slzlo6-J9C7wSDF4dh_kBg"
# 	} 

# Now decrypt......................................

# First, load 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_CkJsonObject $jweRecipientHdr
    delete_CkJsonObject $jweUnprotHdr
    delete_CkJsonObject $jsonTemp
    delete_CkJwe $jwe2
    exit
}

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

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

puts "original text decrypted with AES key wrap key: "
puts "$originalPlaintext"

# ---------------------------------------------------------------------------------
# It should also be possible to decrypt the flattened JWE as shown in RFC 7516, Appendix A.5
# because it was produced using the same key.

set sbJwe [new_CkStringBuilder]

CkStringBuilder_Append $sbJwe "{"
CkStringBuilder_Append $sbJwe "\"protected\":"
CkStringBuilder_Append $sbJwe "\"eyJlbmMiOiJBMTI4Q0JDLUhTMjU2In0\","
CkStringBuilder_Append $sbJwe "\"unprotected\":"
CkStringBuilder_Append $sbJwe "{\"jku\":\"https://server.example.com/keys.jwks\"},"
CkStringBuilder_Append $sbJwe "\"header\":"
CkStringBuilder_Append $sbJwe "{\"alg\":\"A128KW\",\"kid\":\"7\"},"
CkStringBuilder_Append $sbJwe "\"encrypted_key\":"
CkStringBuilder_Append $sbJwe "\"6KB707dM9YTIgHtLvtgWQ8mKwboJW3of9locizkDTHzBC2IlrT1oOQ\","
CkStringBuilder_Append $sbJwe "\"iv\":"
CkStringBuilder_Append $sbJwe "\"AxY8DCtDaGlsbGljb3RoZQ\","
CkStringBuilder_Append $sbJwe "\"ciphertext\":"
CkStringBuilder_Append $sbJwe "\"KDlTtXchhZTGufMYmOYGS4HffxPSUrfmqCHXaI9wOGY\","
CkStringBuilder_Append $sbJwe "\"tag\":"
CkStringBuilder_Append $sbJwe "\"Mz-VPPyU4RlcuYv1IwIvzw\""
CkStringBuilder_Append $sbJwe "}"

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

set recipientIndex 0
CkJwe_SetWrappingKey $jwe2 $recipientIndex $aesWrappingKey "base64url"

set originalPlaintext [CkJwe_decrypt $jwe2 $recipientIndex "utf-8"]
if {[CkJwe_get_LastMethodSuccess $jwe2] != 1} then {
    puts [CkJwe_lastErrorText $jwe2]
    delete_CkJwe $jwe
    delete_CkJsonObject $jweProtHdr
    delete_CkJsonObject $jweRecipientHdr
    delete_CkJsonObject $jweUnprotHdr
    delete_CkJsonObject $jsonTemp
    delete_CkJwe $jwe2
    delete_CkStringBuilder $sbJwe
    exit
}

puts "original text decrypted from published flattened JWE: "
puts "$originalPlaintext"

# The output:

# original text decrypted with AES key wrap key: 
# Live long and prosper.
# original text decrypted from published flattened JWE: 
# Live long and prosper.

delete_CkJwe $jwe
delete_CkJsonObject $jweProtHdr
delete_CkJsonObject $jweRecipientHdr
delete_CkJsonObject $jweUnprotHdr
delete_CkJsonObject $jsonTemp
delete_CkJwe $jwe2
delete_CkStringBuilder $sbJwe