Thom

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seen Nov 1 '12 at 17:42

Nov
1
comment Distinguish messages
I would like to compare the number of strings of length equal or less than $p(n)$ with the number of strings of length $p(n)+n$. Is this a good idea?
Nov
1
revised Proving that a scheme is not IND-CPA-secure
added 35 characters in body
Nov
1
asked Proving that a scheme is not IND-CPA-secure
Oct
31
comment Distinguish messages
I want to show that it is not secure when the messages are of different lengths. My thought was this: suppose that the encryption of a single bit cannot be longer than $p(n)$, what do we know about a message of lets say length $p(n)+n$? My idea was to let the adversary select $m_0 \in \{0,1\}$ and $m_1 \in \{0,1\}^{p(n)+n}$.
Oct
31
comment Distinguish messages
How do I know how big $l_1$ should be? And what is the chance of $m_0$ being encrypted in a ciphertext longer than $l_1$?
Oct
31
awarded  Scholar
Oct
31
accepted Distinguish messages
Oct
31
comment Distinguish messages
Thank you. "Now, suppose you have the two messages $||m_0||=l_0$, $||m_1||=l_1$ and $l_0<<l_1$ (say $l_0=$1bit and $l_1$ is very large >10Gbits). If you receive a ciphertext shorter than $l_1$ you know that $m_1$ was encrypted." I guess you meant $m_0$ in this last sentence?
Oct
30
awarded  Student
Oct
30
asked Distinguish messages
Oct
30
awarded  Editor
Oct
29
comment Modifications of CBC-MAC
@Bob, I still don't understand it. What happens when the message is of length > 2^n?
Oct
29
comment Modifications of CBC-MAC
@bob, will you please explain 3?