[U-Boot] Secure booting using u-boot 2013

[JYOTI DUBEY]

Hello,
        I am trying to perform secure booting on nitrogen 6X SOM using
u-boot 2013. I tried to pad  and sign the u-boot.imx image for
authentication.But the size of both u-boot.imx as well as
u-boot-signed-padded.imx remains same. Technically signed and padded image
should have more size than normal .imx image. Can anyone inform where  and
what changes should I make in the source code of u-boot so that I can solve
the problem?

Thanks in Advance!