The symmetric cryptosystem One time pad (OTP) seems to be very beautiful since i

Question

The symmetric cryptosystem One time pad (OTP) seems to be very beautiful since it is perfectly secret according to Shannon. Many books, however, point out that the main drawback is that one must create a secret key of length as the plaintext. For this reason the concept of perfect secrecy is nowadays abandoned, and we prefer other types of cryptosystems.

Now for example suppose I want to encode my text message with the ASCII scheme, and moreover suppose that this plaintext occupies 10 gigabytes, thus (using OTP) also the key occupies 10 gigabytes. I think however this is a ''sustainable price'' because on the other hand I'm sure that the ciphertext is can't be attacked.

Practically, I don't understand why having such long keys with OTP is a big disavantage even if we reach "the dream" namely the perfect secrecy . Nowadays the storage of informations is very easy, so where is really the problem? I can for example share the "long key" with a physical meeting!

Thanks in advance

Explanation / Answer

Actually, the problem with OTP isn't the storage of the pad (although secure erasure of the parts of the pad you used is trickier than it looks), and it isn't the pad generation (although, again, that's trickier than it looks), but the secure transport.

After all, it's not enough for you (Alice) to have the secure pad, you also have to give a copy to the guy (Bob) you're sending the message to, and you need to send it in a way that's secure.

That's the real reason OTP's aren't used that often; OTP's would require meeting with the other side directly, or alternatively using a trusted courier; we rarely want to put up with the expense with either, especially since there are cheaper alternatives available.

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