diff --git a/test/crypto-layer/CryptoSignaturePrivateKeyHandle.test.ts b/test/crypto-layer/CryptoSignaturePrivateKeyHandle.test.ts
index aed6e0b..2fffe74 100644
--- a/test/crypto-layer/CryptoSignaturePrivateKeyHandle.test.ts
+++ b/test/crypto-layer/CryptoSignaturePrivateKeyHandle.test.ts
@@ -3,26 +3,40 @@ import { CryptoHashAlgorithm, CryptoSignature } from "@nmshd/crypto";
 import { KeyPairSpec } from "@nmshd/rs-crypto-types";
 import { expect } from "chai";
 import { CoreBuffer } from "src/CoreBuffer";
+import { CryptoSignaturePrivateKeyHandle } from "src/crypto-layer/signature/CryptoSignaturePrivateKeyHandle";
 import { CryptoSignatures } from "src/signature/CryptoSignatures";
-import { expectCryptoSignatureKeypairHandle } from "./CryptoSignatureKeypairHandle.test";
+
+export async function expectCryptoSignaturePrivateKeyHandle(
+    value: CryptoSignaturePrivateKeyHandle,
+    id: string,
+    spec: KeyPairSpec,
+    providerName: string
+): Promise<void> {
+    expect(value).to.be.instanceOf(CryptoSignaturePrivateKeyHandle);
+    expect(value.id).to.equal(id);
+    expect(value.providerName).to.equal(providerName);
+    expect(value.spec).to.deep.equal(spec);
+    expect(value.keyPairHandle).to.be.ok;
+    expect(value.provider).to.be.ok;
+    expect(await value.keyPairHandle.id()).to.equal(id);
+    expect(await value.provider.providerName()).to.equal(providerName);
+}
 
 export class CryptoSignaturePrivateKeyHandleTest {
     public static run(): void {
         describe("CryptoSignaturePrivateKeyHandle", function () {
-            describe("sign() with SoftwareProvider", function () {
-                it("sign() and verify() with P256", async function () {
-                    const spec: KeyPairSpec = {
-                        asym_spec: "P256",
-                        cipher: null,
-                        signing_hash: "Sha2_512",
-                        ephemeral: false,
-                        non_exportable: false
-                    };
-                    const cryptoKeyPairHandle = await CryptoSignatures.generateKeypairHandle(
-                        { providerName: "SoftwareProvider" },
-                        spec
-                    );
-                    await expectCryptoSignatureKeypairHandle(cryptoKeyPairHandle, "SoftwareProvider", spec);
+            describe("CryptoSignaturePrivateKeyHandle SoftwareProvider P256 Sha2_512", function () {
+                const spec: KeyPairSpec = {
+                    asym_spec: "P256",
+                    cipher: null,
+                    signing_hash: "Sha2_512",
+                    ephemeral: false,
+                    non_exportable: false
+                };
+                const providerIdent = { providerName: "SoftwareProvider" };
+
+                it("sign and verify", async function () {
+                    const cryptoKeyPairHandle = await CryptoSignatures.generateKeypairHandle(providerIdent, spec);
 
                     const data = new CoreBuffer("0123456789ABCDEF");
                     const signature = await CryptoSignatures.sign(
@@ -41,6 +55,51 @@ export class CryptoSignaturePrivateKeyHandleTest {
                         true
                     );
                 });
+
+                it("toJSON and fromJSON", async function () {
+                    const cryptoKeyPairHandle = await CryptoSignatures.generateKeypairHandle(providerIdent, spec);
+                    const privateKeyHandle = cryptoKeyPairHandle.privateKey;
+                    const id = privateKeyHandle.id;
+                    const providerName = privateKeyHandle.providerName;
+
+                    const serializedPrivateKeyHandle = privateKeyHandle.toJSON();
+                    expect(serializedPrivateKeyHandle).to.be.instanceOf(Object);
+                    expect(serializedPrivateKeyHandle.cid).to.equal(id);
+                    expect(serializedPrivateKeyHandle.pnm).to.equal(providerName);
+                    expect(serializedPrivateKeyHandle.spc).to.deep.equal(spec);
+                    expect(serializedPrivateKeyHandle["@type"]).to.equal("CryptoSignaturePrivateKeyHandle");
+
+                    const loadedPrivateKeyHandle =
+                        await CryptoSignaturePrivateKeyHandle.fromJSON(serializedPrivateKeyHandle);
+                    await expectCryptoSignaturePrivateKeyHandle(loadedPrivateKeyHandle, id, spec, providerName);
+                });
+
+                it("toBase64 and fromBase64", async function () {
+                    const cryptoKeyPairHandle = await CryptoSignatures.generateKeypairHandle(providerIdent, spec);
+                    const privateKeyHandle = cryptoKeyPairHandle.privateKey;
+                    const id = privateKeyHandle.id;
+                    const providerName = privateKeyHandle.providerName;
+
+                    const serializedPrivateKey = privateKeyHandle.toBase64();
+                    expect(serializedPrivateKey).to.be.ok;
+                    const deserializedPrivateKey = CryptoSignaturePrivateKeyHandle.fromBase64(serializedPrivateKey);
+                    await expectCryptoSignaturePrivateKeyHandle(await deserializedPrivateKey, id, spec, providerName);
+                });
+
+                // eslint-disable-next-line jest/expect-expect
+                it("from", async function () {
+                    const cryptoKeyPairHandle = await CryptoSignatures.generateKeypairHandle(providerIdent, spec);
+                    const privateKeyHandle = cryptoKeyPairHandle.privateKey;
+                    const id = privateKeyHandle.id;
+                    const providerName = privateKeyHandle.providerName;
+
+                    const loadedPrivateKeyHandle = await CryptoSignaturePrivateKeyHandle.from({
+                        spec: spec,
+                        id: id,
+                        providerName: providerName
+                    });
+                    await expectCryptoSignaturePrivateKeyHandle(loadedPrivateKeyHandle, id, spec, providerName);
+                });
             });
         });
     }
diff --git a/test/index.ts b/test/index.ts
index d1d8ed0..0f875b8 100644
--- a/test/index.ts
+++ b/test/index.ts
@@ -5,6 +5,7 @@ import {
     getAllProviders,
     getProviderCapabilities
 } from "@nmshd/rs-crypto-node";
+import chai from "chai";
 import { BufferTest } from "./BufferTest.test";
 import { CryptoLayerProviderTest } from "./crypto-layer/CryptoLayerProviderTest.test";
 import { CryptoSignatureKeypairHandleTest } from "./crypto-layer/CryptoSignatureKeypairHandle.test";
@@ -24,6 +25,8 @@ import { CryptoSignatureTest } from "./crypto/CryptoSignature.test";
 import { CryptoStateTest } from "./crypto/CryptoStateTest.test";
 import { SodiumWrapperTest } from "./crypto/SodiumWrapperTest.test";
 
+chai.config.truncateThreshold = 0;
+
 // This is valid: https://mochajs.org/#delayed-root-suite
 // eslint-disable-next-line @typescript-eslint/no-floating-promises
 (async function () {