Re: [Boost-users] boost.Iostream OpenSSL Filter

Subject: Re: [Boost-users] boost.Iostream OpenSSL Filter
From: exocoder (exocoder_at_[hidden])
Date: 2012-08-08 16:47:08

Thank you Wil, Just been studying the example code in the link you
kindly provided. I notice though, that these examples encrypt the entire
file in memory before calling 'EVP_CipherFinal_ex( ... )'. My
understanding is that without calling this function, decryption of the
file will fail. I not sure how compatible this would be with a
boost.Iostream filter, which will write the encrypted data on the fly?

I guess I could just place the data into a memory buffer, and calling
EVP_CypherFinal_ex then writing the data when close is called, but this
feels like an ugly solution, that would break the expected operation of
an iostream.

On Wed, 2012-08-08 at 13:29 -0500, Will Mason wrote:
> Hello,
> 
> On Wed, Aug 8, 2012 at 1:10 PM, exocoder <exocoder_at_[hidden]> wrote:
>         Thank you for the info Neil,
>         I am looking at the example that you pointed to, need to get
>         my head around the issues of
>         initialising/closing OpenSSL in the filter. It seems that
>         every OpenSSL example uses a different
>         interface :(
> 
> 
> I think the OpenSSL EVP interface is the one you
> want: http://www.openssl.org/docs/crypto/EVP_EncryptInit.html#
> 
> 
> Cheers,
> Will
> 
> 
>  
>         Again Thank you for the advice.
>         
>         On Mon, 2012-08-06 at 15:40 -0600, Neil Nelson wrote:
>         > exocoder,
>         >
>         > Upon just reading the docs at
>         >
>         >
>         http://www.boost.org/doc/libs/1_50_0/libs/iostreams/doc/index.html
>         >
>         > and particularly
>         >
>         >      2.2.8. Multi-Character Filters
>         >
>         > It looks like you could take the code from the following
>         page
>         >
>         >
>         http://stackoverflow.com/questions/1007337/encrypting-and-decrypting-a-small-file-using-openssl
>         >
>         > with the critical line being
>         >
>         >      AES_cfb128_encrypt(indata, outdata, bytes_read, &key,
>         ivec, &num,
>         > AES_ENCRYPT);
>         >
>         > that reads and writes to memory buffers. Two other aspects
>         are: (1)
>         > software using encryption is export restricted and you can
>         research that
>         > if needed for your application, (2) key management is likely
>         the more
>         > complicated part, and (3) use of initialization vectors
>         (added random
>         > bytes at the beginning of the input data).
>         >
>         > Neil Nelson
>         >
>         > > I am currently looking at using OpenSSL to write
>         information to an
>         > > encrypted file on-the-fly so to speak. I have been
>         researching my
>         > > options for doing this, and have come across the
>         Boost.Iostream library,
>         > > which promises to be a very elegant solution (The
>         documentation even
>         > > suggests that filters can be written to provide
>         encryption/decryption
>         > > using OpenSSL).
>         > > It would seem that my best approach would be to use the
>         BIO_f* interface
>         > > to encrypt a memory buffer, which could be written by
>         overloading
>         > > write(). However the OpenSSL documentation is particularly
>         sparse when
>         > > it comes to file/memory encryption and I would appreciate
>         any advice on
>         > > how to do this.
>         > > Thank you in advance for any help proffered.
>         >
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>         
>         
>         
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