Creating a Digital Signature

This is a discussion on Creating a Digital Signature within the Linux Programming forums, part of the Platform Specific Boards category; I am developing an application (standalone application) in C that runs on linux platform. I have some problems with some ...

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    Question Creating a Digital Signature

    I am developing an application (standalone application) in C that runs on linux platform. I have some problems with some of the actions in this application such as, (i) Creating a digital signature for a message ,(ii) Encrypting the message and
    (iii) Decrypting the message. Please help me...

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    31173 h4x0r gnu-ehacks's Avatar
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    Well, for 2 and 3, it's very simple. Just make some characters eqal another character. Like, if I were to type in 'i', and you wanted to encrypt it, then make it equal to "es". Then, when the message is recieved, then it will get it as "es", and just convert it to 'i'. I hope you understood this.
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    Originally posted by gnu-ehacks
    Well, for 2 and 3, it's very simple. Just make some characters eqal another character. Like, if I were to type in 'i', and you wanted to encrypt it, then make it equal to "es". Then, when the message is recieved, then it will get it as "es", and just convert it to 'i'. I hope you understood this.
    That's the worst encryption method ever(if it can even be called encryption), and the solution to every one of those letter substitution can be found at your local library, in a damn Sherlock Holmes book.

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    junior member mix0matt's Avatar
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    heh, Sunday word jumble, anyone?

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    ggs
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    C > C++ duders ggs's Avatar
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    For creating a digital signature for a message, try searching for the MD2, MD4 and MD5 algorithms. Probably somewhere on rfc-editor.com...
    .sect signature

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    MD5 0wnz j00
    also don't use simple substitution ciphers for reasons that won't fit in this board., Also don't use simple xor encryption.... *shudders*
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    Registered User zahid's Avatar
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    Hi,
    Encryption algorithm MD2, MD4 and MD5.. DES, the address rfc-editor.com not working.

    Reference from any other site?
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    encryption

    For encryption/decryption/signatures using public key cryptography, I could refer you to the following site

    http://www.openssl.org/docs

    I know it might be pretty much like diving into the middle of an ocean, but persevere, here are some guidelines, look for the following functions

    RSA_size
    RSA_generate_key
    RSA_public_encrypt
    RSA_private_decrypt
    RSA_public_decrypt
    RSA_private_encrypt
    RSA_sign

    The beggining is not that easy, don't expect it to be. As for substitutions, I kind of would not advise it.

    Good Luck.
    -------------------------
    Gerald.

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    encryption

    If your program fails to compile and gives messages like:

    Code:
    tmp/ccMNhYc6.o: In function `main':
    /tmp/ccMNhYc6.o(.text+0x2d): undefined reference to `RSA_generate_key'
    /tmp/ccMNhYc6.o(.text+0x5a): undefined reference to `RSA_size'
    /tmp/ccMNhYc6.o(.text+0x85): undefined reference to `RSA_public_encrypt'
    /tmp/ccMNhYc6.o(.text+0xd3): undefined reference to `RSA_size'
    /tmp/ccMNhYc6.o(.text+0xf5): undefined reference to `RSA_size'
    /tmp/ccMNhYc6.o(.text+0x131): undefined reference to `RSA_private_decrypt'
    try compiling like this

    $ gcc -o <outputname> -lcrypto <programfilename>

    if this doesn't work, start searching for the openssl libraries.
    -------------------------
    Gerald.

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