In pdf 1.7 specification page130, Public-Key Encryption Algorithms section, Figure3.4 shows that a PKCS#7 objects are used to store enveloped data. To decrypt this PKCS#7 object, first step is to use recipient's private key to decrypt this recipient's encrypted key to plain text key. But it does not say what decryption algorithm we should follow to get the plaintext key. I have two question:
1. usually, how long is the private key,1024 bits or 2056 bits or some other length?
2. how to find the decryption algorithm I need to follow to using private key to get the plaintext key? what does this information stored?
Thanks.