diff --git a/docs/pages/reference/main/addToDate.md b/docs/pages/reference/main/addToDate.md
new file mode 100644
index 0000000..53398ff
--- /dev/null
+++ b/docs/pages/reference/main/addToDate.md
@@ -0,0 +1,27 @@
+---
+title: "addToDate()"
+---
+
+# `addToDate()`
+
+Creates a new `Date` by adding the provided time-span to the one provided. Supports negative time spans.
+
+## Definition
+
+```ts
+//$ TimeSpan=/reference/main/TimeSpan
+function createDate(date: Date, timeSpan: $$TimeSpan): Date;
+```
+
+### Parameters
+
+- `date`
+- `timeSpan`
+
+## Example
+
+```ts
+import { addToDate, TimeSpan } from "oslo";
+
+const tomorrow = addToDate(new Date(), new TimeSpan(1, "d"));
+```
diff --git a/docs/pages/reference/main/createDate.md b/docs/pages/reference/main/createDate.md
deleted file mode 100644
index 2822660..0000000
--- a/docs/pages/reference/main/createDate.md
+++ /dev/null
@@ -1,26 +0,0 @@
----
-title: "createDate()"
----
-
-# `createDate()`
-
-Creates a new `Date` by adding the provided time-span to the current time. Mostly for defining expiration times. Supports negative time span.
-
-## Definition
-
-```ts
-//$ TimeSpan=/reference/main/TimeSpan
-function createDate(timeSpan: $$TimeSpan): Date;
-```
-
-### Parameters
-
-- `timeSpan`
-
-## Example
-
-```ts
-import { createDate, TimeSpan } from "oslo";
-
-const tomorrow = createDate(new TimeSpan(1, "d"));
-```
diff --git a/docs/pages/reference/main/index.md b/docs/pages/reference/main/index.md
index 9c8b88c..c20a549 100644
--- a/docs/pages/reference/main/index.md
+++ b/docs/pages/reference/main/index.md
@@ -8,7 +8,7 @@ Provides basic utilities used by other modules.
 
 ## Functions
 
-- [`createDate()`](/reference/main/createDate)
+- [`addToDate()`](/reference/main/addToDate)
 - [`isWithinExpirationDate()`](/reference/main/isWithinExpirationDate)
 
 ## Classes
diff --git a/src/crypto/bytes.test.ts b/src/crypto/bytes.test.ts
new file mode 100644
index 0000000..9177fdd
--- /dev/null
+++ b/src/crypto/bytes.test.ts
@@ -0,0 +1,12 @@
+import { expect, test } from "vitest";
+import { constantTimeEqual } from "./bytes.js";
+
+test("compareBytes()", () => {
+	const randomBytes = new Uint8Array(32);
+	crypto.getRandomValues(randomBytes);
+	expect(constantTimeEqual(randomBytes, randomBytes)).toBe(true);
+	const anotherRandomBytes = new Uint8Array(32);
+	crypto.getRandomValues(anotherRandomBytes);
+	expect(constantTimeEqual(randomBytes, anotherRandomBytes)).toBe(false);
+	expect(constantTimeEqual(new Uint8Array(0), new Uint8Array(1))).toBe(false);
+});
diff --git a/src/crypto/bytes.ts b/src/crypto/bytes.ts
new file mode 100644
index 0000000..1553775
--- /dev/null
+++ b/src/crypto/bytes.ts
@@ -0,0 +1,10 @@
+export function constantTimeEqual(a: Uint8Array, b: Uint8Array): boolean {
+	if (a.length !== b.length) {
+		return false;
+	}
+	let c = 0;
+	for (let i = 0; i < a.length; i++) {
+		c |= a[i]! ^ b[i]!;
+	}
+	return c === 0;
+}
diff --git a/src/crypto/index.ts b/src/crypto/index.ts
index 4c5a25a..3841011 100644
--- a/src/crypto/index.ts
+++ b/src/crypto/index.ts
@@ -1,6 +1,4 @@
-export { ECDSA } from "./ecdsa.js";
-export { HMAC } from "./hmac.js";
-export { RSASSAPKCS1v1_5, RSASSAPSS } from "./rsa.js";
+export { ECDSA, HMAC, RSASSAPKCS1v1_5, RSASSAPSS } from "./signing-algorithm/index.js";
 export { sha1, sha256, sha384, sha512 } from "./sha/index.js";
 export {
 	random,
@@ -9,21 +7,6 @@ export {
 	alphabet,
 	generateRandomBoolean
 } from "./random.js";
+export { constantTimeEqual } from "./bytes.js";
 
-export type { ECDSACurve } from "./ecdsa.js";
-
-export interface KeyPair {
-	publicKey: Uint8Array;
-	privateKey: Uint8Array;
-}
-
-export function constantTimeEqual(a: Uint8Array, b: Uint8Array): boolean {
-	if (a.length !== b.length) {
-		return false;
-	}
-	let c = 0;
-	for (let i = 0; i < a.length; i++) {
-		c |= a[i]! ^ b[i]!;
-	}
-	return c === 0;
-}
+export type { SigningAlgorithm, KeyPair, ECDSACurve } from "./signing-algorithm/index.js";
diff --git a/src/crypto/ecdsa.test.ts b/src/crypto/signing-algorithm/ecdsa.test.ts
similarity index 93%
rename from src/crypto/ecdsa.test.ts
rename to src/crypto/signing-algorithm/ecdsa.test.ts
index 90f471f..3894575 100644
--- a/src/crypto/ecdsa.test.ts
+++ b/src/crypto/signing-algorithm/ecdsa.test.ts
@@ -1,8 +1,8 @@
 import { describe, test, expect } from "vitest";
-import { ECDSA } from "./index.js";
+import { ECDSA } from "../index.js";
 
 import type { ECDSACurve } from "./ecdsa.js";
-import type { SHAHash } from "./sha/index.js";
+import type { SHAHash } from "../sha/index.js";
 
 interface TestCase {
 	hash: SHAHash;
diff --git a/src/crypto/ecdsa.ts b/src/crypto/signing-algorithm/ecdsa.ts
similarity index 90%
rename from src/crypto/ecdsa.ts
rename to src/crypto/signing-algorithm/ecdsa.ts
index 5d654a2..840b802 100644
--- a/src/crypto/ecdsa.ts
+++ b/src/crypto/signing-algorithm/ecdsa.ts
@@ -1,9 +1,9 @@
-import type { KeyPair } from "./index.js";
-import type { SHAHash } from "./sha/index.js";
+import type { SHAHash } from "../sha/index.js";
+import type { SigningAlgorithm, KeyPair } from "./shared.js";
 
 export type ECDSACurve = "P-256" | "P-384" | "P-521";
 
-export class ECDSA {
+export class ECDSA implements SigningAlgorithm {
 	private hash: SHAHash;
 	private curve: ECDSACurve;
 
diff --git a/src/crypto/hmac.test.ts b/src/crypto/signing-algorithm/hmac.test.ts
similarity index 91%
rename from src/crypto/hmac.test.ts
rename to src/crypto/signing-algorithm/hmac.test.ts
index 15df261..cc4a8e1 100644
--- a/src/crypto/hmac.test.ts
+++ b/src/crypto/signing-algorithm/hmac.test.ts
@@ -1,7 +1,7 @@
 import { describe, test, expect } from "vitest";
-import { HMAC } from "./index.js";
+import { HMAC } from "../index.js";
 
-import type { SHAHash } from "./sha/index.js";
+import type { SHAHash } from "../sha/index.js";
 
 interface TestCase {
 	hash: SHAHash;
diff --git a/src/crypto/hmac.ts b/src/crypto/signing-algorithm/hmac.ts
similarity index 87%
rename from src/crypto/hmac.ts
rename to src/crypto/signing-algorithm/hmac.ts
index 87760ee..0dce771 100644
--- a/src/crypto/hmac.ts
+++ b/src/crypto/signing-algorithm/hmac.ts
@@ -1,6 +1,7 @@
-import type { SHAHash } from "./sha/index.js";
+import type { SigningAlgorithm } from "./shared.js";
+import type { SHAHash } from "../sha/index.js";
 
-export class HMAC {
+export class HMAC implements SigningAlgorithm {
 	private hash: SHAHash;
 	constructor(hash: SHAHash) {
 		this.hash = hash;
diff --git a/src/crypto/signing-algorithm/index.ts b/src/crypto/signing-algorithm/index.ts
new file mode 100644
index 0000000..4dfc260
--- /dev/null
+++ b/src/crypto/signing-algorithm/index.ts
@@ -0,0 +1,7 @@
+export { ECDSA } from "./ecdsa.js";
+export { HMAC } from "./hmac.js";
+export { RSASSAPKCS1v1_5, RSASSAPSS } from "./rsa.js";
+
+export type { ECDSACurve } from "./ecdsa.js";
+
+export type { SigningAlgorithm, KeyPair } from "./shared.js";
diff --git a/src/crypto/rsa.test.ts b/src/crypto/signing-algorithm/rsa.test.ts
similarity index 97%
rename from src/crypto/rsa.test.ts
rename to src/crypto/signing-algorithm/rsa.test.ts
index 2018278..cb58c3e 100644
--- a/src/crypto/rsa.test.ts
+++ b/src/crypto/signing-algorithm/rsa.test.ts
@@ -1,7 +1,7 @@
 import { describe, test, expect } from "vitest";
 import { RSASSAPKCS1v1_5, RSASSAPSS } from "./rsa.js";
 
-import type { SHAHash } from "./sha/index.js";
+import type { SHAHash } from "../sha/index.js";
 
 interface TestCase {
 	hash: SHAHash;
diff --git a/src/crypto/rsa.ts b/src/crypto/signing-algorithm/rsa.ts
similarity index 90%
rename from src/crypto/rsa.ts
rename to src/crypto/signing-algorithm/rsa.ts
index 6003e36..b03bb12 100644
--- a/src/crypto/rsa.ts
+++ b/src/crypto/signing-algorithm/rsa.ts
@@ -1,7 +1,7 @@
-import type { KeyPair } from "./index.js";
-import type { SHAHash } from "./sha/index.js";
+import type { KeyPair, SigningAlgorithm } from "./shared.js";
+import type { SHAHash } from "../sha/index.js";
 
-export class RSASSAPKCS1v1_5 {
+export class RSASSAPKCS1v1_5 implements SigningAlgorithm {
 	private hash: SHAHash;
 	constructor(hash: SHAHash) {
 		this.hash = hash;
@@ -132,12 +132,12 @@ export class RSASSAPSS {
 		return signature;
 	}
 
-	public async generateKeyPair(modulusLength?: 2048 | 4096): Promise<KeyPair> {
+	public async generateKeyPair(options?: { modulusLength?: 2048 | 4096 }): Promise<KeyPair> {
 		const cryptoKeyPair = await crypto.subtle.generateKey(
 			{
 				name: "RSA-PSS",
 				hash: this.hash,
-				modulusLength: modulusLength ?? 2048,
+				modulusLength: options?.modulusLength ?? 2048,
 				publicExponent: new Uint8Array([0x01, 0x00, 0x01])
 			},
 			true,
diff --git a/src/crypto/signing-algorithm/shared.ts b/src/crypto/signing-algorithm/shared.ts
new file mode 100644
index 0000000..d5bb062
--- /dev/null
+++ b/src/crypto/signing-algorithm/shared.ts
@@ -0,0 +1,9 @@
+export interface SigningAlgorithm {
+	sign(key: Uint8Array, data: Uint8Array): Promise<Uint8Array>;
+	verify(key: Uint8Array, signature: Uint8Array, data: Uint8Array): Promise<boolean>;
+}
+
+export interface KeyPair {
+	publicKey: Uint8Array;
+	privateKey: Uint8Array;
+}
diff --git a/src/index.ts b/src/index.ts
index 903b792..ea26155 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1,46 +1,3 @@
-export type TimeSpanUnit = "ms" | "s" | "m" | "h" | "d" | "w";
+export { TimeSpan, isWithinExpirationDate, addToDate } from "./time.js";
 
-export class TimeSpan {
-	constructor(value: number, unit: TimeSpanUnit) {
-		this.value = value;
-		this.unit = unit;
-	}
-
-	public value: number;
-	public unit: TimeSpanUnit;
-
-	public milliseconds(): number {
-		if (this.unit === "ms") {
-			return this.value;
-		}
-		if (this.unit === "s") {
-			return this.value * 1000;
-		}
-		if (this.unit === "m") {
-			return this.value * 1000 * 60;
-		}
-		if (this.unit === "h") {
-			return this.value * 1000 * 60 * 60;
-		}
-		if (this.unit === "d") {
-			return this.value * 1000 * 60 * 60 * 24;
-		}
-		return this.value * 1000 * 60 * 60 * 24 * 7;
-	}
-
-	public seconds(): number {
-		return this.milliseconds() / 1000;
-	}
-
-	public transform(x: number): TimeSpan {
-		return new TimeSpan(Math.round(this.milliseconds() * x), "ms");
-	}
-}
-
-export function isWithinExpirationDate(date: Date): boolean {
-	return Date.now() < date.getTime();
-}
-
-export function createDate(timeSpan: TimeSpan): Date {
-	return new Date(Date.now() + timeSpan.milliseconds());
-}
+export type { TimeSpanUnit } from "./time.js";
diff --git a/src/jwt/index.test.ts b/src/jwt/index.test.ts
index 1309a70..4f07496 100644
--- a/src/jwt/index.test.ts
+++ b/src/jwt/index.test.ts
@@ -1,9 +1,9 @@
 import { describe, test, expect } from "vitest";
 import { createJWT, parseJWT, validateJWT } from "./index.js";
 
-import { HMAC } from "../crypto/hmac.js";
-import { ECDSA } from "../crypto/ecdsa.js";
-import { RSASSAPKCS1v1_5, RSASSAPSS } from "../crypto/rsa.js";
+import { HMAC } from "../crypto/signing-algorithm/hmac.js";
+import { ECDSA } from "../crypto/signing-algorithm/ecdsa.js";
+import { RSASSAPKCS1v1_5, RSASSAPSS } from "../crypto/signing-algorithm/rsa.js";
 import { TimeSpan } from "../index.js";
 
 test.each(["ES256", "ES384", "ES512"] as const)(
diff --git a/src/jwt/index.ts b/src/jwt/index.ts
index c0df005..577271e 100644
--- a/src/jwt/index.ts
+++ b/src/jwt/index.ts
@@ -3,6 +3,7 @@ import { base64url } from "../encoding/index.js";
 import { isWithinExpirationDate } from "../index.js";
 
 import type { TimeSpan } from "../index.js";
+import type { SigningAlgorithm } from "../crypto/index.js";
 
 export type JWTAlgorithm =
 	| "HS256"
@@ -235,7 +236,7 @@ export interface JWT extends JWTProperties {
 	parts: [header: string, payload: string, signature: string];
 }
 
-function getAlgorithm(algorithm: JWTAlgorithm): ECDSA | HMAC | RSASSAPKCS1v1_5 | RSASSAPSS {
+function getAlgorithm(algorithm: JWTAlgorithm): SigningAlgorithm {
 	if (algorithm === "ES256" || algorithm === "ES384" || algorithm === "ES512") {
 		return new ECDSA(ecdsaDictionary[algorithm].hash, ecdsaDictionary[algorithm].curve);
 	}
diff --git a/src/oauth2/index.ts b/src/oauth2/index.ts
index 9f2e1f6..1ef9a3a 100644
--- a/src/oauth2/index.ts
+++ b/src/oauth2/index.ts
@@ -1,6 +1,6 @@
 import { sha256 } from "../crypto/index.js";
 import { base64, base64url } from "../encoding/index.js";
-import { createDate, TimeSpan } from "../index.js";
+import { TimeSpan, addToDate } from "../index.js";
 
 export class OAuth2Client {
 	public clientId: string;
@@ -237,7 +237,7 @@ export class OAuth2TokenRevocationClient {
 			const retryAfterNumber = parseInt(retryAfterHeader);
 			if (!Number.isNaN(retryAfterNumber)) {
 				throw new OAuth2TokenRevocationRetryError({
-					retryAfter: createDate(new TimeSpan(retryAfterNumber, "s"))
+					retryAfter: addToDate(new Date(), new TimeSpan(retryAfterNumber, "s"))
 				});
 			}
 			const retryAfterDate = parseDateString(retryAfterHeader);
@@ -303,15 +303,6 @@ export interface TokenResponseBody {
 	scope?: string;
 }
 
-export interface OAuth2Endpoints {
-	authorizeEndpoint: string;
-	tokenEndpoint: string;
-}
-
-export interface OAuth2EndpointsWithTokenRevocation extends OAuth2Endpoints {
-	tokenRevocationEndpoint: string;
-}
-
 function parseDateString(dateString: string): Date | null {
 	try {
 		return new Date(dateString);
diff --git a/src/otp/hotp.ts b/src/otp/hotp.ts
index 69c818d..9a523c0 100644
--- a/src/otp/hotp.ts
+++ b/src/otp/hotp.ts
@@ -1,5 +1,5 @@
 import { bigEndian } from "../binary/uint.js";
-import { HMAC } from "../crypto/hmac.js";
+import { HMAC } from "../crypto/signing-algorithm/hmac.js";
 
 export async function generateHOTP(
 	key: Uint8Array,
diff --git a/src/time.ts b/src/time.ts
new file mode 100644
index 0000000..be22358
--- /dev/null
+++ b/src/time.ts
@@ -0,0 +1,46 @@
+export type TimeSpanUnit = "ms" | "s" | "m" | "h" | "d" | "w";
+
+export class TimeSpan {
+	constructor(value: number, unit: TimeSpanUnit) {
+		this.value = value;
+		this.unit = unit;
+	}
+
+	public value: number;
+	public unit: TimeSpanUnit;
+
+	public milliseconds(): number {
+		if (this.unit === "ms") {
+			return this.value;
+		}
+		if (this.unit === "s") {
+			return this.value * 1000;
+		}
+		if (this.unit === "m") {
+			return this.value * 1000 * 60;
+		}
+		if (this.unit === "h") {
+			return this.value * 1000 * 60 * 60;
+		}
+		if (this.unit === "d") {
+			return this.value * 1000 * 60 * 60 * 24;
+		}
+		return this.value * 1000 * 60 * 60 * 24 * 7;
+	}
+
+	public seconds(): number {
+		return this.milliseconds() / 1000;
+	}
+
+	public transform(x: number): TimeSpan {
+		return new TimeSpan(Math.round(this.milliseconds() * x), "ms");
+	}
+}
+
+export function isWithinExpirationDate(date: Date): boolean {
+	return Date.now() < date.getTime();
+}
+
+export function addToDate(date: Date, timeSpan: TimeSpan): Date {
+	return new Date(date.getTime() + timeSpan.milliseconds());
+}