TLS server authentication certificates validating to the following Entrust roots whose earliest Signed Certificate Timestamp (SCT) is dated after October 31, 2024, will no longer be trusted by default.
On Wednesday, March 13, 2024, Let’s Encrypt generated 10 new Intermediate CA Key Pairs, and issued 15 new Intermediate CA Certificates containing the new public keys.
We created 5 new 2048-bit RSA intermediate certificates named in sequence from R10 through R14. These are issued by ISRG Root X1. You can think of them as direct replacements for our existing R3 and R4 intermediates.
We also created 5 new P-384 ECDSA intermediate certificates named in sequence from E5 through E9. Each of these is represented by two certificates: one issued by ISRG Root X2 (exactly like our existing E1 and E2), and one issued (or cross-signed) by ISRG Root X1.
所以總共是產生了 10 組 intermediate certificate，然後簽了 15 組 intermediate CA 出來。
Let’s Encrypt announced that the cross-signed chain is set to expire on September 30th, 2024. As a result, Cloudflare will stop issuing certificates from the cross-signed CA chain on May 15th, 2024.
Most SSL/TLS certificates (rds-ca-2019) for your DB instances will expire in 2024 after the certificate update in 2020. In December 2022, we released new CA certificates that are valid for 40 years (rds-ca-rsa2048-g1) and 100 years (rds-ca-rsa4096-g1 and rds-ca-ecc384-g1). So, if you rotate your CA certificates, you don’t need to do It again for a long time.
Issuer: (CA ID: 276)
commonName = DST Root CA X3
organizationName = Digital Signature Trust Co.
Validity
Not Before: Jan 20 19:14:03 2021 GMT
Not After : Sep 30 18:14:03 2024 GMT
Subject: (CA ID: 7394)
commonName = ISRG Root X1
organizationName = Internet Security Research Group
countryName = US
On Thursday, Feb 8th, 2024, we will stop providing the cross-sign by default in requests made to our /acme/certificate API endpoint. For most Subscribers, this means that your ACME client will configure a chain which terminates at ISRG Root X1, and your webserver will begin providing this shorter chain in all TLS handshakes. The longer chain, terminating at the soon-to-expire cross-sign, will still be available as an alternate chain which you can configure your client to request.
On Thursday, June 6th, 2024, we will stop providing the longer cross-signed chain entirely. This is just over 90 days (the lifetime of one certificate) before the cross-sign expires, and we need to make sure subscribers have had at least one full issuance cycle to migrate off of the cross-signed chain.
最後就是過期的日子 2024/09/30：
On Monday, September 30th, 2024, the cross-signed certificate will expire. This should be a non-event for most people, as any client breakages should have occurred over the preceding six months.
通常 root CA 的憑證不會直接拿來簽最終使用者使用的憑證 (leaf certificate)，而是 root CA 的憑證先簽 intermediate CA 的憑證，然後 intermediate CA 可能有好幾層一路簽下來，到最後面再用 intermediate CA 的憑證簽最終使用者使用的憑證。
這次公告的內容就題到了，之前的 intermediate CA 是一個固定範圍的量，而且會確保 renew 時用的 intermediate CA 跟先前的是相同的：
Before this change, Amazon maintained a limited number of intermediate CAs and issued and renewed certificates from the same intermediate CAs.
這次則是會變成動態：
With this change, leaf certificates issued to you will be signed by different intermediate CAs.
生效日期是這個月十一日，其實已經生效了：
Starting October 11, 2022 at 9:00 AM Pacific Time, public certificates obtained through ACM will be issued from one of the multiple intermediate CAs that Amazon manages.
官方有提到一個有可能的情況：如果你的應用程式有設定 certificate pinning 的話，應該是對 root CA 設定，而非對 intermediate CA 或是 leaf 做：
If you use intermediate CA information through certificate pinning, you will need to make changes and pin to an Amazon Trust Services root CA instead of an intermediate CA or leaf certificate.
這個也算通則，因為就 certificate pinning 想要做到的效果，對 root CA 做就就行了...
Though the postOfficeBox field is permissible for inclusion in OV certificates, any field containing unvalidated information is not permissible. Furthermore, the EV Guidelines prohibit this field at all for EV certificates.
