(Tcl) Validate a JWS Using ECDSA P-256 SHA-256

Validates a JSON Web Signature (JWS) that uses ECDSA P-256 SHA-256

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

Chilkat Tcl Extension Downloads Chilkat Tcl Extension Downloads

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.

# This example takes a JSON signature in compact serialization format,
# and uses an ECDSA public key to validate and recover the protected header and payload.

# We only need a public key for signature validation.  This is the ECDSA public key
# that is used:

#      {"kty":"EC", 
#       "crv":"P-256", 
#       "x":"f83OJ3D2xF1Bg8vub9tLe1gHMzV76e8Tus9uPHvRVEU", 
#       "y":"x_FEzRu9m36HLN_tue659LNpXW6pCyStikYjKIWI5a0" 
#      } 

set sbPubKey [new_CkStringBuilder]

CkStringBuilder_Append $sbPubKey "{\"kty\":\"EC\","
CkStringBuilder_Append $sbPubKey "\"crv\":\"P-256\","
CkStringBuilder_Append $sbPubKey "\"x\":\"f83OJ3D2xF1Bg8vub9tLe1gHMzV76e8Tus9uPHvRVEU\","
CkStringBuilder_Append $sbPubKey "\"y\":\"x_FEzRu9m36HLN_tue659LNpXW6pCyStikYjKIWI5a0\""
CkStringBuilder_Append $sbPubKey "}"

set pubKey [new_CkPublicKey]

set success [CkPublicKey_LoadFromString $pubKey [CkStringBuilder_getAsString $sbPubKey]]
if {$success != 1} then {
    puts [CkPublicKey_lastErrorText $pubKey]
    delete_CkStringBuilder $sbPubKey
    delete_CkPublicKey $pubKey
    exit
}

set jws [new_CkJws]

# Set the ECC public key:
set signatureIndex 0
CkJws_SetPublicKey $jws $signatureIndex $pubKey

# Load the JWS.
set sbJws [new_CkStringBuilder]

CkStringBuilder_Append $sbJws "eyJhbGciOiJFUzI1NiJ9"
CkStringBuilder_Append $sbJws "."
CkStringBuilder_Append $sbJws "eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFt"
CkStringBuilder_Append $sbJws "cGxlLmNvbS9pc19yb290Ijp0cnVlfQ"
CkStringBuilder_Append $sbJws "."
CkStringBuilder_Append $sbJws "DtEhU3ljbEg8L38VWAfUAqOyKAM6-Xx-F4GawxaepmXFCgfTjDxw5djxLa8ISlSA"
CkStringBuilder_Append $sbJws "pmWQxfKTUJqPP3-Kg6NU1Q"

set success [CkJws_LoadJwsSb $jws $sbJws]
if {$success != 1} then {
    puts [CkJws_lastErrorText $jws]
    delete_CkStringBuilder $sbPubKey
    delete_CkPublicKey $pubKey
    delete_CkJws $jws
    delete_CkStringBuilder $sbJws
    exit
}

# Validate the 1st (and only) signature at index 0..
set v [CkJws_Validate $jws $signatureIndex]
if {$v < 0} then {
    # Perhaps Chilkat was not unlocked or the trial expired..
    puts "Method call failed for some other reason."
    puts [CkJws_lastErrorText $jws]
    delete_CkStringBuilder $sbPubKey
    delete_CkPublicKey $pubKey
    delete_CkJws $jws
    delete_CkStringBuilder $sbJws
    exit
}

if {$v == 0} then {
    puts "Invalid signature.  The ECC key was incorrect, the JWS was invalid, or both."
    delete_CkStringBuilder $sbPubKey
    delete_CkPublicKey $pubKey
    delete_CkJws $jws
    delete_CkStringBuilder $sbJws
    exit
}

# If we get here, the signature was validated..
puts "Signature validated."
puts "--"

# Recover the original content:
puts "Recovered content:"
puts [CkJws_getPayload $jws utf-8]
puts "--"

# Examine the protected header:
# joseHeader is a CkJsonObject
set joseHeader [CkJws_GetProtectedHeader $jws $signatureIndex]
if {[CkJws_get_LastMethodSuccess $jws] != 1} then {
    puts "No protected header found at the given index."
    delete_CkStringBuilder $sbPubKey
    delete_CkPublicKey $pubKey
    delete_CkJws $jws
    delete_CkStringBuilder $sbJws
    exit
}

CkJsonObject_put_EmitCompact $joseHeader 0

puts "Protected (JOSE) header:"
puts [CkJsonObject_emit $joseHeader]
delete_CkJsonObject $joseHeader

# Output:

# 	Signature validated.
# 	--
# 	Recovered content:
# 	{"iss":"joe",
# 	 "exp":1300819380,
# 	 "http://example.com/is_root":true}
# 	--
# 	Protected (JOSE) header:
# 	{ 
# 	  "alg": "ES256"
# 	}

delete_CkStringBuilder $sbPubKey
delete_CkPublicKey $pubKey
delete_CkJws $jws
delete_CkStringBuilder $sbJws