diff --git a/dist/index.cjs b/dist/index.cjs
index 7be0246..6c8cf8f 100644
--- a/dist/index.cjs
+++ b/dist/index.cjs
@@ -87,6 +87,7 @@ __export(src_exports, {
   rsaASN1AlgorithmIdentifier: () => rsaASN1AlgorithmIdentifier,
   signAsDraftToRequest: () => signAsDraftToRequest,
   signatureHeaderIsDraft: () => signatureHeaderIsDraft,
+  splitPer64Chars: () => splitPer64Chars,
   validateAndProcessParsedDraftSignatureHeader: () => validateAndProcessParsedDraftSignatureHeader,
   validateRequestAndGetSignatureHeader: () => validateRequestAndGetSignatureHeader,
   verifyDigestHeader: () => verifyDigestHeader,
@@ -349,6 +350,13 @@ function genSignInfo(parsed, defaults = {
   }
   throw new KeyValidationError("Unknown algorithm");
 }
+function splitPer64Chars(str) {
+  const result = [];
+  for (let i = 0; i < str.length; i += 64) {
+    result.push(str.slice(i, i + 64));
+  }
+  return result;
+}
 
 // src/pem/pkcs8.ts
 var import_asn1js3 = __toESM(require("@lapo/asn1js"), 1);
@@ -719,11 +727,11 @@ function parseRequestSignature(request, options) {
 // src/keypair.ts
 async function exportPublicKeyPem(key) {
   const ab = await globalThis.crypto.subtle.exportKey("spki", key);
-  return "-----BEGIN PUBLIC KEY-----\n" + encodeArrayBufferToBase64(ab) + "\n-----END PUBLIC KEY-----\n";
+  return "-----BEGIN PUBLIC KEY-----\n" + splitPer64Chars(encodeArrayBufferToBase64(ab)).join("\n") + "\n-----END PUBLIC KEY-----\n";
 }
 async function exportPrivateKeyPem(key) {
   const ab = await globalThis.crypto.subtle.exportKey("pkcs8", key);
-  return "-----BEGIN PRIVATE KEY-----\n" + encodeArrayBufferToBase64(ab) + "\n-----END PRIVATE KEY-----\n";
+  return "-----BEGIN PRIVATE KEY-----\n" + splitPer64Chars(encodeArrayBufferToBase64(ab)).join("\n") + "\n-----END PRIVATE KEY-----\n";
 }
 async function genRsaKeyPair(modulusLength = 4096, keyUsage = ["sign", "verify"]) {
   const keyPair = await globalThis.crypto.subtle.generateKey(
@@ -1007,6 +1015,7 @@ async function verifyDraftSignature(parsed, publicKeyPem, errorLogger) {
   rsaASN1AlgorithmIdentifier,
   signAsDraftToRequest,
   signatureHeaderIsDraft,
+  splitPer64Chars,
   validateAndProcessParsedDraftSignatureHeader,
   validateRequestAndGetSignatureHeader,
   verifyDigestHeader,
diff --git a/dist/index.mjs b/dist/index.mjs
index 38a5b21..48c5ace 100644
--- a/dist/index.mjs
+++ b/dist/index.mjs
@@ -252,6 +252,13 @@ function genSignInfo(parsed, defaults = {
   }
   throw new KeyValidationError("Unknown algorithm");
 }
+function splitPer64Chars(str) {
+  const result = [];
+  for (let i = 0; i < str.length; i += 64) {
+    result.push(str.slice(i, i + 64));
+  }
+  return result;
+}
 
 // src/pem/pkcs8.ts
 import ASN13 from "@lapo/asn1js";
@@ -622,11 +629,11 @@ function parseRequestSignature(request, options) {
 // src/keypair.ts
 async function exportPublicKeyPem(key) {
   const ab = await globalThis.crypto.subtle.exportKey("spki", key);
-  return "-----BEGIN PUBLIC KEY-----\n" + encodeArrayBufferToBase64(ab) + "\n-----END PUBLIC KEY-----\n";
+  return "-----BEGIN PUBLIC KEY-----\n" + splitPer64Chars(encodeArrayBufferToBase64(ab)).join("\n") + "\n-----END PUBLIC KEY-----\n";
 }
 async function exportPrivateKeyPem(key) {
   const ab = await globalThis.crypto.subtle.exportKey("pkcs8", key);
-  return "-----BEGIN PRIVATE KEY-----\n" + encodeArrayBufferToBase64(ab) + "\n-----END PRIVATE KEY-----\n";
+  return "-----BEGIN PRIVATE KEY-----\n" + splitPer64Chars(encodeArrayBufferToBase64(ab)).join("\n") + "\n-----END PRIVATE KEY-----\n";
 }
 async function genRsaKeyPair(modulusLength = 4096, keyUsage = ["sign", "verify"]) {
   const keyPair = await globalThis.crypto.subtle.generateKey(
@@ -909,6 +916,7 @@ export {
   rsaASN1AlgorithmIdentifier,
   signAsDraftToRequest,
   signatureHeaderIsDraft,
+  splitPer64Chars,
   validateAndProcessParsedDraftSignatureHeader,
   validateRequestAndGetSignatureHeader,
   verifyDigestHeader,
diff --git a/dist/utils.d.ts b/dist/utils.d.ts
index 572c7c8..bea5185 100644
--- a/dist/utils.d.ts
+++ b/dist/utils.d.ts
@@ -32,3 +32,4 @@ export declare function genSignInfo(parsed: ParsedAlgorithmIdentifier, defaults?
     hash: SignatureHashAlgorithmUpperSnake;
     ec: 'DSA' | 'DH';
 }): SignInfo;
+export declare function splitPer64Chars(str: string): string[];
diff --git a/package.json b/package.json
index ce9164b..7a06864 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@misskey-dev/node-http-message-signatures",
-  "version": "0.0.0-alpha.16",
+  "version": "0.0.0-alpha.17",
   "description": "",
   "type": "module",
   "keywords": [
diff --git a/src/keypair.ts b/src/keypair.ts
index 389d64b..4c55b0d 100644
--- a/src/keypair.ts
+++ b/src/keypair.ts
@@ -4,20 +4,20 @@
  */
 
 import type { webcrypto as crypto } from 'node:crypto';
-import { encodeArrayBufferToBase64 } from './utils';
+import { encodeArrayBufferToBase64, splitPer64Chars } from './utils';
 import { ECNamedCurve } from './types';
 
 export async function exportPublicKeyPem(key: crypto.CryptoKey) {
 	const ab = await globalThis.crypto.subtle.exportKey('spki', key);
 	return '-----BEGIN PUBLIC KEY-----\n' +
-		encodeArrayBufferToBase64(ab) +
+		splitPer64Chars(encodeArrayBufferToBase64(ab)).join('\n') +
 		'\n-----END PUBLIC KEY-----\n';
 }
 
 export async function exportPrivateKeyPem(key: crypto.CryptoKey) {
 	const ab = await globalThis.crypto.subtle.exportKey('pkcs8', key);
 	return '-----BEGIN PRIVATE KEY-----\n' +
-		encodeArrayBufferToBase64(ab) +
+	splitPer64Chars(encodeArrayBufferToBase64(ab)).join('\n') +
 		'\n-----END PRIVATE KEY-----\n';
 }
 
diff --git a/src/utils.test.ts b/src/utils.test.ts
index a515e51..16131ec 100644
--- a/src/utils.test.ts
+++ b/src/utils.test.ts
@@ -1,4 +1,5 @@
-import { genASN1Length } from "./utils";
+import { genASN1Length, splitPer64Chars } from "./utils";
+import { rsa4096 } from "../test/keys";
 
 describe(genASN1Length, () => {
 	test('10', () => {
@@ -14,3 +15,13 @@ describe(genASN1Length, () => {
 		expect(genASN1Length(1145141919810)).toEqual(Uint8Array.from([0x86, 1, 10, 159, 199, 0, 66]));
 	});
 });
+
+describe(splitPer64Chars, () => {
+	test('short', () => {
+		expect(splitPer64Chars('a').length).toBe(1);
+		expect(splitPer64Chars('a')[0]).toBe('a');
+	});
+	test('normal', () => {
+		expect(splitPer64Chars(rsa4096.privateKey).length).toBe(Math.ceil(rsa4096.privateKey.length / 64));
+	});
+});
diff --git a/src/utils.ts b/src/utils.ts
index 93471ff..9ac1fa9 100644
--- a/src/utils.ts
+++ b/src/utils.ts
@@ -113,3 +113,11 @@ export function genSignInfo(
 	}
 	throw new KeyValidationError('Unknown algorithm');
 }
+
+export function splitPer64Chars(str: string): string[] {
+	const result = [] as string[];
+	for (let i = 0; i < str.length; i += 64) {
+		result.push(str.slice(i, i + 64));
+	}
+	return result;
+}