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Thread: Reverse RSA encryption???

  1. #1

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    PowerPoster i00's Avatar
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    Reverse RSA encryption???

    RSA encryption has a singing (public) key and a reading (private) key...

    EDIT:
    Just a disclaimer: I am not wanting to reverse engineer RSA ...
    I am just wanting to know if there is a crypto algorithm that allows the signing to be the private part
    END EDIT

    However both keys need to contain the signing key to be able to read the data...

    I was wondering if there is a secure crypto method for generating a private and public key from a server having the signing key being the private key and the public key used to read the data??

    ... the problem with RSA (in this regard) is, since it requires the reading key to also contain the signing key, this would mean that the user could also create an encrypted key...

    I want data in my program that can be read by the user but not created by them...

    Any Ideas?
    Thanks,
    Kris

  2. #2
    Super Moderator Shaggy Hiker's Avatar
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    Re: Reverse RSA encryption???

    Quote Originally Posted by i00 View Post
    RSA encryption has a singing (public) key and a reading (private) key...

    Kris
    Not all singing should be public, but if it is, it had best be on key.
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  3. #3

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    Re: Reverse RSA encryption???

    Quote Originally Posted by Shaggy Hiker View Post
    Not all singing should be public, but if it is, it had best be on key.
    Shaggy this is basically how RSA works:
    I use the term public loosely - as does the spec by design ... the public key is not really public it is public in the term that the end target does not have the private key...
    a different key is usually issued to each endpoint ... keys are issued both ways between each end point (this issuing is also encrypted)...
    the server issues one to the client and the client issues one to the server ... the server signs with the clients public key and the client signs with the servers public key ... this way the intended endpoints are the only ones that can read the data.

    Kris

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    Super Moderator Shaggy Hiker's Avatar
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    Re: Reverse RSA encryption???

    You may have thought I was being serious, but I was pointing out your interesting spelling of the word "signing".
    My usual boring signature: Nothing

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    Re: Reverse RSA encryption???

    Quote Originally Posted by Shaggy Hiker View Post
    You may have thought I was being serious, but I was pointing out your interesting spelling of the word "signing".
    Ahh lol ... it makes sense now ... I thought it was some bad English and didn't really know what u meant (I should have realized coming from you since you that it wasn't this )... miss-read it as being signing when you re-posted..

    ... good one

    K

  6. #6
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    Re: Reverse RSA encryption???

    Keys are just numbers. The properties are the same. Any key can be used for signing. That is, if you use the public key to sign/encrypt, it is the private key that can decrypt/verify.

    The term "private" denotes it is the one that only some trusted individual/entity is supposed to possess. If you can decrypt a message with a public key, you can be reasonably certain it was encrypted with the private key. That's how digital signing works, when you verify the signature you know the only way it can be verified is if the trusted individual's private key signed it.

    Of course, if that private key is held by NOT trusted individuals, trust is broken.

    I don't think you're right that the "private key contains the public key". It is true that one key derives from the other, but it is not supposed to be a reversible operation. That is, if one could easily (or even with difficulty) deduce the private key from the public key, RSA would be compromised and not trustworthy.

    But because public keys happen to be "a number" and the only requirement of an encryption key is "a number", you ask for the impossible. To get what you're asking for, you'd have to find an encryption algorithm with more specific private key requirements. That's... not a good idea, because the more numbers can be excluded as "bad" private keys the more easy it becomes to derive or guess private keys.

    Or at least that's how I interpret your question.
    This answer is wrong. You should be using TableAdapter and Dictionaries instead.

  7. #7
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    Re: Reverse RSA encryption???

    an asymmetric algorithm like RSA can be used for encryption of data and for signatures. the public keypart is always, as the name suggests, public so you share that specific "magic" numbers.

    now, if you want to sign data, you use your private key to encrypt a hash of the data to create the signature. anyone can calculate the hash from the data themself, then take the signature data and decrypt it with your public key. if both hashes match then the following things are proved: a) it was you singing with your private key and b) the data is unmodified and exactly what you signed.

    using an asymmetric algorithm for encryption is the other way around. here you want to encrypt data so that only one specific person can decrypt it. so you take the public key of that person and encrypt the data with it. after that, it can only be decrypted with the matching private key.

    so, an asymmetric encryption is a one way function using "e" to create something that can only be reconstructed using "d". for signature you keep e private and share d, for allowing someone to send you encrypted messages, you keep d private and share e.

    is that what you mean with reverse?
    Last edited by digitalShaman; Apr 21st, 2018 at 04:06 PM.

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