Question: What is the relationship between the **EMV** **ODA**, **CA** and issuer certificate during the transaction?

Answer: 
Data Authentication is used for validating authenticity of an EMV payment card when the request for payment is received on POC. The [EMV CA](https://emvca.com/index.html#EMV-CA) is used for generating EMV root certificates and issuing EMV Issuer certificates for banks that issue payment cards to their customers. Index of CA Public key, issuer certificate, and SDA signature with card holder data are sent to the POC, which can then get the CA public key from the POS storage, use the CA Public key to verify the Issuer RSA key in Issuer Certificate, and use the issuer RSA key to decrypt the SDA Signature and verify that what was signed is the same to the card data. In this process also EMV CA CRL, and EMV Issuer CRL is used for validating whether the certificates are not revoked.
* You should use CA public key to decrypt issuer public key certificate (tag 0x90)
* The decrypted data format is in EMV 4.3 book 2 Retrieval of Issuer Public Key