# Re: Encryption key longer than text to encrypt

*From*: run_signature_script_for_my_email@xxxxxxxxxxx (laura fairhead)*Date*: Wed, 03 Jan 2007 17:30:36 GMT

On Wed, 03 Jan 2007 16:44:30 +0000, rossum <rossum48@xxxxxxxxxxxx> wrote:

On 3 Jan 2007 06:41:46 -0800, "Jean-François Michaud"

<cometaj@xxxxxxxxxxx> wrote:

Since it is easier in practice to use pseudo random data than to

generate random data which is then distributed as appropriate if we

have OTP in mind, would

encrypting messages à la OTP with 'pseudo random data' using a key

greater than the message make any sense to increase security,

No. The reason that an OTP is provably secure is that the keystream

is truly random. As soon as you substitute a pseudo-random keystream

the security proof fails. You no longer have an OTP, you have a

stream cypher instead.

Hi,

I always wonder about this "provably secure". I don't remember seeing

a convincing proof of security for OTP, does anyone have any references?

For example, a true random number generator could on one particular run

generate a sequence entirely of zeros. Examining the data would then

reveal the original cleartext. Yes it's extremely unlikely to happen

in practise I know (in practise it's probably much more unlikely to happen

than it should even in theory). But it's because of the chance of that

and then a whole series of progressively weaker cases that I would be

inclined to think OTP really isn't 100% secure ...

bestwishes

l

--

echo alru_aafriehdah@xxxxxxxxxx |sed 's/\(.\)\(.\)/\2\1/g'

.

**Follow-Ups**:**Re: Encryption key longer than text to encrypt***From:*rossum

**Re: Encryption key longer than text to encrypt***From:*Unruh

**Re: Encryption key longer than text to encrypt***From:*Jean-François Michaud

**References**:**Encryption key longer than text to encrypt***From:*Jean-François Michaud

**Re: Encryption key longer than text to encrypt***From:*rossum

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