# What Is Root Certificate? Definition and Examples

> Root certificates are self-signed CA certificates that sit at the top of a certificate chain and are pre-installed in trust stores as trust anchors.

Source: https://ssl.sh/glossary/root-certificate/
Last updated: 2026-11-10

A root certificate is the [self-signed](https://ssl.sh/glossary/self-signed-certificate/) certificate for a certificate authority's top-level key: its issuer and subject are the same, and nothing above it vouches for it. Clients trust it only because an operating system, browser or administrator placed it in their [trust store](https://ssl.sh/glossary/trust-store/). Root keys are kept offline in hardware security modules and are used mainly to sign [intermediate certificates](https://ssl.sh/glossary/intermediate-certificate/) and CRLs.

## Why it matters
Every publicly trusted TLS certificate ultimately depends on a root in the client's store, so adding or removing a root changes what millions of devices accept. The Baseline Requirements forbid signing subscriber certificates directly with a root key, which is why chains have intermediates. Roots are long-lived, often 20 years or more, and root programs now push rotation: the Chrome Root Program removes roots whose key material is more than 15 years old on a schedule. Let's Encrypt, for example, introduced ISRG Root YR (RSA-4096) and ISRG Root YE (ECDSA P-384) in its Generation Y hierarchy.

## Example
```bash
openssl x509 -in root.pem -noout -subject -issuer
```

For a root, the subject and issuer lines are identical.

## Common misconceptions
- **The server must send the root certificate.** Clients already have it; a root sent by the server is not trusted just because it appears in the chain, and it only adds bytes to the handshake.
- **Installing a root certificate is harmless.** A root you install can vouch for any website on that device, which is how corporate TLS inspection and some malware intercept HTTPS.
- **Root and intermediate certificates are interchangeable files.** A root is a trust anchor stored on the client; an intermediate must be served by the server, and mixing them up causes chain errors.

## Related terms

- [证书颁发机构](https://ssl.sh/zh/glossary/certificate-authority/): 证书颁发机构（CA）是负责审核申请者、签发数字证书，并把公钥与域名或身份绑定在一起的机构。
- [信任库](https://ssl.sh/zh/glossary/trust-store/): 信任库是操作系统、浏览器或编程语言运行时内置的一组根 CA 证书，验证证书链时以它们作为信任锚。
- [中间证书](https://ssl.sh/zh/glossary/intermediate-certificate/): 中间证书是由根证书（或上级中间证书）签发、用来签发网站证书的 CA 证书，服务器必须把它和网站证书一起发送给客户端。
- [自签名证书](https://ssl.sh/zh/glossary/self-signed-certificate/): 自签名证书是用自身私钥签名的证书，颁发者与主体相同，没有任何 CA 为它担保。
- [证书链](https://ssl.sh/zh/glossary/certificate-chain/): 证书链是从网站终端证书经中间证书一直到受信任根证书的有序证书序列，每一张都由下一张签名。
- [交叉签名](https://ssl.sh/zh/glossary/cross-signing/): 交叉签名是指由一个已被广泛信任的 CA 为另一个 CA 的现有密钥签发证书，使后者签发的证书也能链到老设备信任的根。
- [根证书计划](https://ssl.sh/zh/glossary/root-program/): 根证书计划是浏览器或操作系统厂商用来决定其信任库收录、限制或移除哪些根 CA 的政策与流程。
- [HSM](https://ssl.sh/zh/glossary/hsm/): HSM 是一种防篡改的硬件设备，在内部生成、保存并使用密钥，私钥不会以明文形式离开设备。