How do you reverse the certificate blocks given a CER file using a linux script?

How do you reverse the certificate blocks given a CER file using a linux script (i.e. awk, sed, etc..) ?

So suppose I have a file called mycert.cer that looks like:

-----BEGIN CERTIFICATE-----
this is sentence1
this is sentence2
-----END CERTIFICATE-----
-----BEGIN CERTIFICATE-----
this is sentence3
this is sentence4
-----END CERTIFICATE-----
-----BEGIN CERTIFICATE-----
this is sentence5
this is sentence6
-----END CERTIFICATE-----
-----BEGIN CERTIFICATE-----
this is sentence7
this is sentence8
-----END CERTIFICATE-----

I want the output to look like:

-----BEGIN CERTIFICATE-----
this is sentence7
this is sentence8
-----END CERTIFICATE-----
-----BEGIN CERTIFICATE-----
this is sentence5
this is sentence6
-----END CERTIFICATE-----
-----BEGIN CERTIFICATE-----
this is sentence3
this is sentence4
-----END CERTIFICATE-----
-----BEGIN CERTIFICATE-----
this is sentence1
this is sentence2
-----END CERTIFICATE-----

I have tried the following:

tac -s'-----BEGIN CERTIFICATE-----' mycert.cer | awk '/-----BEGIN CERTIFICATE-----/, /-----END CERTIFICATE-----/'

but this command gave the following incorrect output:

-----BEGIN CERTIFICATE-----
this is sentence3
this is sentence4
-----END CERTIFICATE-----
-----BEGIN CERTIFICATE-----
this is sentence1
this is sentence2
-----END CERTIFICATE-----
-----BEGIN CERTIFICATE----------BEGIN CERTIFICATE-----

How do I fix the command so that I get the desired output?

Using any awk plus tac:

$ tac mysert.cer | awk '
    { cert = $0 ORS cert }
    /BEGIN CERT/ { printf "%s", cert; cert="" }
'
-----BEGIN CERTIFICATE-----
this is sentence7
this is sentence8
-----END CERTIFICATE-----
-----BEGIN CERTIFICATE-----
this is sentence5
this is sentence6
-----END CERTIFICATE-----
-----BEGIN CERTIFICATE-----
this is sentence3
this is sentence4
-----END CERTIFICATE-----
-----BEGIN CERTIFICATE-----
this is sentence1
this is sentence2
-----END CERTIFICATE-----

or just awk:

$ awk '
    { cert = cert $0 ORS }
    /END CERT/ { certs[++numCerts] = cert; cert="" }
    END { for (i=numCerts; i>=1; i--) printf "%s", certs[i] }
' mycert.cer
-----BEGIN CERTIFICATE-----
this is sentence7
this is sentence8
-----END CERTIFICATE-----
-----BEGIN CERTIFICATE-----
this is sentence5
this is sentence6
-----END CERTIFICATE-----
-----BEGIN CERTIFICATE-----
this is sentence3
this is sentence4
-----END CERTIFICATE-----
-----BEGIN CERTIFICATE-----
this is sentence1
this is sentence2
-----END CERTIFICATE-----

In awk:

awk 'BEGIN{RS="";ORS=FS="-----END CERTIFICATE-----\n"}{while(--NF)print $NF}' file
# or slightly longer
awk -v RS="" -v FS="-----END CERTIFICATE-----\n" '{while(--NF)printf "%s",$NF FS}' file

# or you ever find an awk that doesn't allow changing NF (I haven't)
# change action to for(i=NF;--i;)print $i resp printf "%s%,$i FS

In perl:

perl -n0777e 'map{print}reverse split $\="-----END CERTIFICATE-----\n"' file

Both of these treat the whole file as one 'record' and if your awk is not GNU (fairly rare nowadays but not unknown) it might fail for a too-large file.