I understand that SSL certs cannot be signed using SHA-1 anymore. Yet, all CA root certificates are SHA-1 signed (mostly). Does it mean the same algorithm that is no longer trusted for "you grandma SSL shop" is fine for the uttermost top secured certificate of the world?
Am I missing something? (key usage? key size?)
Best Answer
The signature of the root CA certificates do not matter at all, since there is no need to verify them. They are all self-signed.
If you trust a root CA certificate, there’s no need to verify its signature. If you don’t trust it, its signature is worthless for you.
Edit: there are some very relevant comments below. I don’t feel comfortable copying or rephrasing them and taking credit for them instead of their authors. But I welcome people to add explanations to this answer.