Digital signatures are a crucial application of hash functions, like SHA-256, to ensure the authenticity and integrity of data. In the context of SSL/TLS certificates, digital signatures play a vital role in:

1. Authenticating the identity of the certificate holder (e.g., a website).

2. Ensuring the integrity of the certificate contents (e.g., public key, identity information).

3. Preventing tampering or alteration of the certificate.

4. Verifying the certificate's issuance and validity.

The digital signature scheme in SSL/TLS certificates typically involves:

1. Hashing the certificate contents using a hash function like SHA-256.

2. Encrypting the resulting hash value with the private key of the Certificate Authority (CA).

3. Verifying the signature by decrypting it with the CA's public key and comparing the resulting hash value with a new hash of the certificate contents.

This process ensures that the certificate has not been tampered with or altered during transmission, and that it indeed comes from a trusted CA. Digital signatures, enabled by hash functions like SHA-256, are a fundamental building block of secure online communication.