One Time Pad Low Bandwidth Doubt from the book Following is a sentence from the book &quot;Cryptography and Network Security - Principle and Practices&quot; by William Stallings [Fourth Edition]
Sentence -
&quot;
... the 'one-time pad' is of limited utility, and is useful primarily for low bandwidth channels requiring very high security.
&quot;
Can anyone please elaborate on low bandwidth , because I thing low bandwidth will make transfer of the key and ciphertext slower instead they should use high bandwidth isn't?
Book Link - http://uru.ac.in/uruonlinelibrary/Cyber_Security/Cryptography_and_Network_Security.pdf
Page Number - 79/983
For an OTP you need to distribute the OTP key stream out of band. That can be performed by e.g. bringing a data storage device to the other side. Let me explain.
The problem with an OTP key stream is that you cannot transport it over a secure transport channel without removing the claim of theoretical security. Similarly, you cannot simply distribute a seed for a PRNG, because the PRNG would have similar security as a stream cipher.
Because you cannot distribute an OTP without compromising its security it is limited to the amount of information that you distributed out of band.
How limiting this is depends on the application of course. Nowadays you can store several TB in a tiny flash disk. That's enough for many, many hours of video. Still, securely distributing such a disk would be troublesome; just sending it by regular post is obviously not a good option.
Another option would be to use quantum key distribution. However, implementations of quantum key distributions are not necessarily secure, and the speed may be a severe limit.
Fortunately, we've got a lot of ciphers that we don't know how to break, key ratchets and whatnot to give us practical security even for much smaller key sizes.