# RSA low exponent with padded plain-text

Considering a case, when modulus is large and hard to factor, exponent e=3 and there is a cipher-text which is created by padding plain-text with A's from left and the ride side such that the real plain-text lies in the very center.

Which attacks could apply in such case. Low-Exponent Cube root attack fails. Does the knowledge of some part of the plain-text such as A's become helpful ?

• So you encrypt AAAAAA+2^k m, where k can take only a few values. If we know k, we can multiply the cryptotext by 2^{-k} and now have the crypto of something of the form well-known + something small – Hagen von Eitzen Apr 21 '19 at 7:04
• @HagenvonEitzen Assume that the message is 1 bit and assume that the right padding is $n/2$-bit and left is $n/2-1$-bit. If you multiply the ciphertext by $2^{-n/2}$ you will get $n/2+1$-bit ciphertext. If you take the power 3 then the result will be clearly more than $n$-bit. – kelalaka Apr 21 '19 at 16:09