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NOTE: Pardon my ignorance of encryption, I learned about these concepts today

Going to rephrase this question, but I think I already have fine answers provided. I need to have a block of data containing a message (user imputed) that is included in what I want to encrypt. I also need to have some means of authenticating the user, such as a password. The password will most likely be hashed for extra security. I am considering using a RSA public and private key pair of which the attacker can know, but wont be able to use, as he/she will need to authenticate themselves with a password of which they cannot know. Both the message (which I do not want the attacker to know) and the hashed password will be included inside the RSA encrypted data block (aka: RSA('message block', sha256('password')) ). Right now, my main question is if this is secure or not.

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closed as too broad by e-sushi, fkraiem, DrLecter, yyyyyyy, cpast Jun 16 '15 at 13:22

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

  • $\begingroup$ What is it that the server [knows or [can do]] that the attacker [[doesn't know] or [can't do]]? $\:$ What is it that the client [knows or [can do]] that the attacker [[doesn't know] or [can't do]]? $\;\;\;\;$ $\endgroup$ – user991 Jun 16 '15 at 0:28
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if you want to use a password, SRP is probably a good choice. alternatively, you could use ECDHE with ECDSA or RSA keys. you should also use a MAC of some sort if you're using CBC (and encrypt then MAC). GCM or OCB would be much better choices.

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There is multiple solutions that's more sophisticated than this one. But you could easy authenticate the user if you have a secret that both the server and the client knows. By using the HMAC protocol example: 

SHA256 ( SHA256 ( data_before_encryption ) + secret )

You create a hash of the the data you are sending before you encrypt it, and then you append the secret to that hash, and then create a new hash from the old hash + secret. The server can authenticate the user by doing the same operation after the data is decrypted. You can use SHA256 to this.

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    $\begingroup$ thats not how HMAC works $\endgroup$ – Richie Frame Jun 16 '15 at 1:13
  • $\begingroup$ Clarification with your answer and the one above, would a scheme such as this "rsa ( 'non-credential data' + sha256('password/sensitive data') ) " be a secure scheme to use? $\endgroup$ – user373043 Jun 16 '15 at 8:18

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