Script using Crypt::CBC encryption/decryption

[vermarajeev]

Hello friends,

I am new to Perl scripts.
Please help me out....

I am using crypt::CBC to encrypt my files...

during decryption process it goes through the code as follows

if ($header_mode eq 'salt') {
    my ($salt) = $$input_stream =~ /^Salted__(.{8})/s;
    croak "Ciphertext does not begin with a valid header for 'salt' header mode" unless defined $salt;
    $self->{salt} = $salt;          # new salt
    substr($$input_stream,0,16) = '';
    my ($key,$iv) = $self->_salted_key_and_iv($self->{passphrase},$salt);
    $self->{iv} = $self->{civ}  = $iv;
    $self->{key}  = $key;
}
 

my ($salt) = $$input_stream =~ /^Salted__(.{8})/s;
 

Can anybody tell me what the above instruction means....

sub _salted_key_and_iv {
    my $self = shift;
    my ($pass,$salt)  = @_;
 
    croak "Salt must be 8 bytes long" unless length $salt == 8;
 
    my $key_len = $self->{keysize};
    my $iv_len  = $self->{blocksize};
 
    my $desired_len = $key_len+$iv_len;
 
    my $data  = '';
    my $d = '';
 
    while (length $data < $desired_len) {
        $d = md5($d . $pass . $salt);
        $data .= $d;
    }
    return (substr($data,0,$key_len),substr($data,$key_len,$iv_len));
}
 

How are they retrieve the password and the iv

Thanks,
Rajeev

[pbmods]

Heya, Rajeev.

I'm going to go ahead and move this thread to the Perl forum, where our resident Experts will be better able to help you out.

[miller]

my ($salt) = $$input_stream =~ /^Salted__(.{8})/s;
 

Can anybody tell me what the above instruction means....

Rajeev,

It assigns $salt to the 8 characters after Salted__ from the string $$input_stream.

I suggest that you read Crypt::CBC instead of simply using someone else's script. You'll find more clear usage description in there, and they are also 3 example scripts included in the distribution. You'll find links to them at the bottom of the cpan doc.

- Miller

[numberwhun]

Rajeev,

It assigns $salt to the 8 characters after Salted__ from the string $$input_stream.

I suggest that you read Crypt::CBC instead of simply using someone else's script. You'll find more clear usage description in there, and they are also 3 example scripts included in the distribution. You'll find links to them at the bottom of the cpan doc.

- Miller

Welcome back miller! How was your trip?

Jeff