Hi Amit,
For this issue, I recommend to go to Internet Information Service(IIS) and click the IIS site for the corresponding web application in SharePoint 2010.
Then click IIS Settings to select Ignore under Client certificates.
If you do not want to set it to Ignore, then you need to get a client certificate from the CA for the crawl account and then define the crawl rule to specify the client certificate.
Or you can create a new web app that only uses NTLM (e.g. not having the "Require Client Certificate" enabled) for crawling and then extend into a new zone with https where this "Require Client Certificate" could be enabled.
Best regards,
Victoria