for the following protocol: $(1)$ A $->$ B: nA

$(2)$ B $->$ A: CertB, nB$,$ SB$($nA$,$ nB$),(3)$ A $->$ B: CertA, SA$($nB$,$ nA$),$ Where nA$$

and nB are arbitrary numbers that can only be used once, chosen by A $($Alicia$)$ and B $($Benito$),$ SA and SB are the signature algorithms of Alicia and Benito respectively, and CertA and CertB are certificates, authenticating the public keys of Alicia and Benito, respectively. However, Carlos found an attack by which he could authenticate himself as Alicia to Benito. Explain the details of how Carlos achieved this. Include aids like diagrams or equations.