Ok, thanks.
> -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] Behalf Of Dr. Stephen Henson > Sent: Sunday, September 28, 2003 8:37 PM > To: [EMAIL PROTECTED] > Subject: Re: 3-DES size > > > On Sun, Sep 28, 2003, Pierre De Boeck wrote: > > > I would like to know the overhead in size when encrypting > > a message of n bytes with 3DES. > > > > A simple rule of thumb says that it will be n bytes plus > > the padding needed for n to be a multiple of 64 bits (8 bytes). > > > > Is it correct? and how the different modes (CBC,..)+ initialization > > vector influences that rule? > > Block ciphers encrypt data in multiples of the block size so if > the input data > isn't a multiple of the block size it has to be padded. > > Standard block padding (aka PKCS#5 padding) adds k bytes each of > value k where > > k = block_size - input_size%block_size > > note this means that if the input is already a multiple of the > block size then > block_size bytes are added. This is so the decrypter can unambiguously > determine the size of the input data. > > That assumes standard block padding. You can disable standard > block padding > in the EVP calls but then you have to provide your own scheme to > ensure the > input is a multiple of the block size. > > Steve. > -- > Dr Stephen N. Henson. > Core developer of the OpenSSL project: http://www.openssl.org/ > Freelance consultant see: http://www.drh-consultancy.demon.co.uk/ > Email: [EMAIL PROTECTED], PGP key: via homepage. > ______________________________________________________________________ > OpenSSL Project http://www.openssl.org > User Support Mailing List [EMAIL PROTECTED] > Automated List Manager [EMAIL PROTECTED] ______________________________________________________________________ OpenSSL Project http://www.openssl.org User Support Mailing List [EMAIL PROTECTED] Automated List Manager [EMAIL PROTECTED]
