okp.rb in cose-1.3.0

- old
+ new

@@ -1,7 +1,8 @@
 # frozen_string_literal: true
 
+require "cose/key/curve"
 require "cose/key/curve_key"
 require "openssl"
 
 module COSE
   module Key
@@ -12,11 +13,58 @@
         if map[LABEL_KTY] != KTY_OKP
           raise "Not an OKP key"
         end
       end
 
+      def self.from_pkey(pkey)
+        curve = Curve.by_pkey_name(pkey.oid) || raise("Unsupported edwards curve #{pkey.oid}")
+        attributes = { crv: curve.id }
+
+        asymmetric_key = pkey.public_to_der
+        public_key_bit_string = OpenSSL::ASN1.decode(asymmetric_key).value.last.value
+        attributes[:x] = public_key_bit_string
+        begin
+          asymmetric_key = pkey.private_to_der
+          private_key = OpenSSL::ASN1.decode(asymmetric_key).value.last.value
+          curve_private_key = OpenSSL::ASN1.decode(private_key).value
+          attributes[:d] = curve_private_key
+        rescue OpenSSL::PKey::PKeyError
+          # work around lack of https://github.com/ruby/openssl/pull/527, otherwise raises this error
+          # with message 'i2d_PKCS8PrivateKey_bio: error converting private key' for public keys
+          nil
+        end
+
+        new(**attributes)
+      end
+
       def map
         super.merge(LABEL_KTY => KTY_OKP)
+      end
+
+      def to_pkey
+        if curve
+          private_key_algo = OpenSSL::ASN1::Sequence.new(
+            [OpenSSL::ASN1::ObjectId.new(curve.pkey_name)]
+          )
+          seq = if d
+                  version = OpenSSL::ASN1::Integer.new(0)
+                  curve_private_key = OpenSSL::ASN1::OctetString.new(d).to_der
+                  private_key = OpenSSL::ASN1::OctetString.new(curve_private_key)
+                  [version, private_key_algo, private_key]
+                else
+                  public_key = OpenSSL::ASN1::BitString.new(x)
+                  [private_key_algo, public_key]
+                end
+
+          asymmetric_key = OpenSSL::ASN1::Sequence.new(seq)
+          OpenSSL::PKey.read(asymmetric_key.to_der)
+        else
+          raise "Unsupported curve #{crv}"
+        end
+      end
+
+      def curve
+        Curve.find(crv)
       end
     end
   end
 end