> On 10/25/2011 10:52 AM, Jonas Schnelli wrote:
>> How do i create a HMAC-SHA1 with a RSA Key?
>> What do i give as input for the param *key?
>>
>> Why:
>> My encrypted file has now the filename of the unencrypted-files-sha1.
>> (unsecure!).
>> I cannot use the sha1 of the encrypted file because i use EVP_Seal* (aes256
>> session key) so the sha1 of the encrypted file will change after every
>> encryption (need to be constant because of the other function in the
>> project).
>> My approach is, to use a encrypted sha1 of the unencrypted file (so it might
>> keep constant).
>> I also tried to use RSA_public_encrypt on the unencrypted sha1, but i'd like
>> to avoid 128BIT filenames.
>>
>>
> From your question, I gather that you want the following:
>
> Give the encrypted file a (short) file name which is computed from the
> unencrypted plaintext in a way that adversaries cannot use to determine
> if the plaintext is the same as some guessed value, or which otherwise
> helps adversaries.
>
> It is OK if only the encrypting party can generate the file name
> (otherwise an adversary could calculate it too).
>
> Proposed solution.
>
> 1. Generate a secret 224 bit key and store it somewhere safe (as safely
> as you store your RSA private keys).
>
> 2. Use this secret key as the key when computing HMAC-SHA224 of
> the unencrypted plaintext.
Another thing:
Can i also just make a HMAC-SSH224 of the SHA1 of the unencrypted plaintext
instead of the whole plaintext?
Is this to unsafe?
Remember: i just want to have a filename which not leads to a possible
file-content.
Thanks
>
> 3. Convert the resulting 224 bit value to a string using Base32 or another
> scheme of your choosing. (Base32 would produce a 45 character
> case insensitive string).
>
> 4. Truncate the string to your desired file name length, but not so short
> that accidental collisions become likely (Example to keep up to 16000
> file names likely different, use file names with 2 * log2(16000)=2*14=28
> bits minimum).
>
> --
> Jakob Bohm, CIO, WiseMo A/S.
> Secure remote control of Smart phones, PCs and embedded systems.
> This public posting comes with no promises, no warranties and is not binding.
>
> ______________________________________________________________________
> OpenSSL Project http://www.openssl.org
> User Support Mailing List openssl-users@openssl.org
> Automated List Manager majord...@openssl.org
