openssl - is RSA private key less than public? -
When I create a pair of RSA by OpenSL, it seems that the private key (personal exponent) is always less than the public key (modulus). ). Is it from RSA Design?
This is not a requirement, but there is no reason to grow it compared to modulus: < / P>
Personal exponent d
is calculated to satisfy the public exponent e
and the modulus n
:
ed ≡ 1 mod φ (n)
Now, if we believe that d & gt; Φ (n)
, then we can define d '= d mod φ (n)
, and not only d' & lt; Φ (n)
, but the above relationship still holds, that is:
ed '≡ 1 mod φ (n)
Thus D '
is also a valid private exponent, and since φ (n)
d '
should also be less than n
.
Since a large private investor needs more storage, and (at least nostalgic implementation) decryption slows down, the least possible private exponent is most suitable.