He's referring to the fact that with ECDSA signatures, if the randomness is bad on a single signature (i.e. you know the "k" value in the signature) then that i

He's referring to the fact that with ECDSA signatures, if the randomness is bad on a single signature (i.e. you know the "k" value in the signature) then that is sufficient to reveal the private key used in making the signature. Similarly, if two signatures are made with the same nonce and private key, you can reveal the nonce and thus the private key. The maths is actually explained on the wiki page: https://en.wikipedia.org/wiki/Elliptic_Curve_Digital_Signature_Algorithm https://en.wikipedia.org/wiki/Elliptic_Curve_Digital_Signatu...