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Interval for PKCS#1 v1.5 compliant plaintext

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In Bleichenbacher's paper (http://archiv.infsec.ethz.ch/education/fs08/secsem/bleichenbacher98.pdf, section 3.1) he concludes that if m*s is PKCS#1 v1.5 compliant we get the following interval:

$2B \leq m\cdot s \bmod n < 3B$.

(k is the length of n in bits, $ B = 2^{8*(k-2)}$)

Given those bytes in the range, 3 to 11 may not contain any zero bytes, and at least one zero bytes follows from byte 11, can we use a smaller interval?

Maarten Bodewes avatar
in flag
The most significant byte is still between 01 and FF, so for a continuous interval you might start a bit higher I suppose. However, there is a 02 valued byte in front of it, which means you'd shave off 1/1024th from the interval. As we're talking about bytes, not bits, the next random byte 01 to FF will shave off 1/(256*1024). Sounds all pretty insignificant to me.
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