fixup! test(TPM::KeyAttestation#key): returns nil when t_public curve…

…_id differs from key curve_id

spec/tpm/key_attestation_spec.rb

@@ -361,6 +361,7 @@
       let(:root_key) { create_ecc_key(key_curve_id) }
       let(:attestation_key) { create_ecc_key(key_curve_id) }
       let(:attested_key) { create_ecc_key(key_curve_id) }
+      let(:key_curve_id) { TPM::ECC_NIST_P256 }
 
       let(:signature_algorithm) { TPM::ALG_ECDSA }
       let(:hash_algorithm) { TPM::ALG_SHA256 }
@@ -387,7 +388,6 @@
         let(:scheme) { TPM::ALG_NULL }
 
         context "when t_public.parameters and t_public.unique are compatible" do
-          let(:key_curve_id) { TPM::ECC_NIST_P256 }
           let(:t_public_curve_id) { TPM::ECC_NIST_P256 }
 
           it "returns a public ECDSA key with the correct properties" do
@@ -398,8 +398,9 @@
         end
 
         context "when t_public.parameters and t_public.unique are incompatible" do
-          let(:key_curve_id) { TPM::ECC_NIST_P256 }
-          let(:t_public_curve_id) { TPM::ECC_NIST_P256 + 1 }
+          # Make the curve in t_public.parameters different than the curve
+          # used to generate the coordinates of the t_public.unique field
+          let(:t_public_curve_id) { TPM::ECC_NIST_P384 }
 
           it "returns nil" do
             expect(key_attestation.key).to be nil