# PostSignum Root QCA 4 root certificate (PostSignum)

> PostSignum Root QCA 4 is a root CA certificate operated by PostSignum (RSA 4096, valid until 2038-07-26, SHA-256 AC7F7862). As of the latest CCADB data it is trusted for TLS server authentication by 1 of 4 major root stores: Microsoft.

Source: https://ssl.sh/roots/postsignum-root-qca-4/
Last updated: 2026-11-10

PostSignum Root QCA 4 is a root CA certificate operated by PostSignum (RSA 4096, valid until 2038-07-26, SHA-256 AC7F7862). As of the latest CCADB data it is trusted for TLS server authentication by 1 of 4 major root stores: Microsoft.

| Field | Value |
|---|---|
| CA owner | PostSignum |
| Subject | CN=PostSignum Root QCA 4,O=Česká pošta\, s.p.,2.5.4.97=NTRCZ-47114983,C=CZ |
| SHA-256 | AC7F7862E685C7A7D9826A58EA32D183D4893FCC8F8FD6D900C9769A987E77F0 |
| SPKI SHA-256 | C372F6D18EBEE5AA23D9E919F3E6BE98488EC01607DF3162FC192E4B1346AFB3 |
| Valid from | 2018-07-26 |
| Expires | 2038-07-26 |
| Key | RSA 4096 |
| Signature algorithm | sha512WithRSAEncryption |
| Serial number | FA0 |
| SHA-1 (Windows thumbprint) | AA40D2579BA82424CD27719B1D6B1F3571738099 |

## Root store status

| Root store | Status | Trusted for TLS | Distrust for TLS after | Details |
|---|---|---|---|---|
| Chrome | Not included | No | - | - |
| Mozilla | Not included | No | - | - |
| Apple | Not included | No | - | - |
| Microsoft | Included | Yes | - | Trusted EKUs: Server Authentication, Client Authentication, Document Signing, OCSP Signing, Secure Email, Time Stamping; Not-before cutoff: 2019-10-01 (OCSP Signing); Disallowed EKUs: OCSP Signing |

The CCADB lists no EV policy OID for PostSignum Root QCA 4.

## Intermediate CAs issued by this root

The CCADB lists 2 intermediate CA certificates signed directly by PostSignum Root QCA 4: 2 currently valid, 0 expired and 0 revoked (revoked includes those whose parent was revoked).

| Intermediate | Operated by | Expires | Status | SHA-256 |
|---|---|---|---|---|
| PostSignum Public CA 4 | PostSignum | 2033-09-27 | Valid | E4272DFA3FBC48C90929518A0482BA3D9EB9C94A3CD397139F0ECDF2475955F6 |
| PostSignum Qualified CA 4 | PostSignum | 2033-09-27 | Valid | 4779BA66C768FE7E5A5BB74A225FA8B69CD6942AF481355630E5AD78B34DFF2B |

## Cross-signed versions

No certificate in the CCADB has the same subject and public key as PostSignum Root QCA 4 with a different issuer, so a client has to carry PostSignum Root QCA 4 itself in its root store to trust it.


## What happens when it expires

PostSignum Root QCA 4 is valid until 2038-07-26, about 11.7 years after this data snapshot (2026-11-10). From that day, browsers and operating systems that check trust-anchor expiry stop accepting chains that end at this root, so any certificate that can only chain to it fails validation. Android is a known exception: it does not enforce the expiry date of trust anchors.

## FAQ

**Is PostSignum Root QCA 4 trusted by Chrome, Firefox, Safari and Windows?**

As of 2026-11-10, Microsoft trust it for TLS server authentication; Chrome, Mozilla, Apple do not.

**When does PostSignum Root QCA 4 expire?**

On 2038-07-26, about 11.7 years after the 2026-11-10 data snapshot.

**How many intermediate certificates has PostSignum Root QCA 4 issued?**

The CCADB lists 2: 2 valid, 0 expired and 0 revoked. The newest valid one is PostSignum Public CA 4, valid until 2033-09-27.

**Is PostSignum Root QCA 4 cross-signed?**

No. The CCADB has no certificate with the same subject and public key signed by another CA.

Sources: CCADB TLS Server Authentication report, All Included Root Certificate Trust Bit Settings, All Certificate Information (V5), the per-store TLS reports and Mozilla's Included CA Certificate Report (ccadb.org/resources).