find out what the script is with that wget line and amend it so it includes --no-check-certificate
The Debian side of things requires that you find out what the script is and edit it as described above. Or update Debian, maybe your Debian or an aspect of it is out of date. Or maybe the instructions you read were out of date.
It looks like perhaps the instructions you read were out of date. I don't think running knoppix64 or knoppix would make a difference. And personally, at the initial bootup screen when i've used Knoppix. I have always pushed ENTER and it loaded the right one on the 32-bit laptop I ran it on. There is also a config file to automatically type something at that screen. But I don't think that has anything to do with this error you're getting.
I think the instructions you read for installing it were just out of date. Here is the incorrect, and the correct, wget command
Notice that the incorrect command says To connect to people.debian.org insecurely, use
--no-check-certificate'.` So that should lead you to see the correct command is one that has that switch.
Here's the wget side of things.
Notice the difference between the command that fails and the command that works
FAILS
C:\treesize>wget http://people.debian.org/~bartm/flashplugin-nonfree/get-upstrea
m-version.pl.gz.pgp
SYSTEM_WGETRC = c:/progra~1/wget/etc/wgetrc
syswgetrc = c:\program files\gnuwin32/etc/wgetrc
--2014-08-02 16:04:06-- http://people.debian.org/~bartm/flashplugin-nonfree/get
-upstream-version.pl.gz.pgp
Resolving people.debian.org... 5.153.231.30
Connecting to people.debian.org|5.153.231.30|:80... connected.
HTTP request sent, awaiting response... 301 Moved Permanently
Location: https://people.debian.org/~bartm/flashplugin-nonfree/get-upstream-vers
ion.pl.gz.pgp [following]
--2014-08-02 16:04:06-- https://people.debian.org/~bartm/flashplugin-nonfree/ge
t-upstream-version.pl.gz.pgp
Connecting to people.debian.org|5.153.231.30|:443... connected.
ERROR: cannot verify people.debian.org's certificate, issued by `/C=FR/O=GANDI S
AS/CN=Gandi Standard SSL CA':
Unable to locally verify the issuer's authority.
To connect to people.debian.org insecurely, use `--no-check-certificate'.
Unable to establish SSL connection.
WORKS
C:\treesize>wget http://people.debian.org/~bartm/flashplugin-nonfree/get-upstrea
m-version.pl.gz.pgp --no-check-certificate
SYSTEM_WGETRC = c:/progra~1/wget/etc/wgetrc
syswgetrc = c:\program files\gnuwin32/etc/wgetrc
--2014-08-02 16:04:15-- http://people.debian.org/~bartm/flashplugin-nonfree/get
-upstream-version.pl.gz.pgp
Resolving people.debian.org... 5.153.231.30
Connecting to people.debian.org|5.153.231.30|:80... connected.
HTTP request sent, awaiting response... 301 Moved Permanently
Location: https://people.debian.org/~bartm/flashplugin-nonfree/get-upstream-vers
ion.pl.gz.pgp [following]
--2014-08-02 16:04:16-- https://people.debian.org/~bartm/flashplugin-nonfree/ge
t-upstream-version.pl.gz.pgp
Connecting to people.debian.org|5.153.231.30|:443... connected.
WARNING: cannot verify people.debian.org's certificate, issued by `/C=FR/O=GANDI
SAS/CN=Gandi Standard SSL CA':
Unable to locally verify the issuer's authority.
HTTP request sent, awaiting response... 200 OK
Length: 1872 (1.8K) [application/pgp-encrypted]
Saving to: `get-upstream-version.pl.gz.pgp'
100%[======================================>] 1,872 --.-K/s in 0s
2014-08-02 16:04:16 (14.2 MB/s) - `get-upstream-version.pl.gz.pgp' saved [1872/1
872]
Also, I recognize there may be an issue with adobe flash being non-free(not open source and thus somewhat excommunicated), but it may be possible to install it with apt-get or aptitude. A google suggested Trying sudo apt-get install flashplugin-installer