This worked for me:
[root@Maleah trix]# perl -MCPAN -e 'install Crypt::RSA'CPAN: Storable
+loaded ok
Going to read /root/.cpan/Metadata
CPAN: LWP::UserAgent loaded okFetching with LWP:
ftp://carroll.cac.psu.edu/pub/CPAN/modules/03modlist.data.gz
Fetching with Net::FTP:
ftp://carroll.cac.psu.edu/pub/CPAN/modules/03modlist.data.gz
Going to read /root/.cpan/sources/modules/03modlist.data.gz
Going to write /root/.cpan/Metadata
Running install for module Crypt::RSA
Running make for V/VI/VIPUL/Crypt-RSA-1.25.tar.gz
Fetching with LWP:
ftp://carroll.cac.psu.edu/pub/CPAN/authors/id/V/VI/VIPUL/Crypt-RSA-1.
+25.tar.gz
Fetching with Net::FTP:
ftp://carroll.cac.psu.edu/pub/CPAN/authors/id/V/VI/VIPUL/Crypt-RSA-1
+.25.tar.gz
Couldn't login on carroll.cac.psu.edu at /usr/lib/perl5/5.6.0/CPAN.pm
+line 2072.
Fetching with LWP:
ftp://cpan.in-span.net/authors/id/V/VI/VIPUL/Crypt-RSA-1.25.tar.gz
Scanning cache /root/.cpan/build for sizes
CPAN: MD5 loaded ok
Fetching with LWP:
ftp://cpan.in-span.net/authors/id/V/VI/VIPUL/CHECKSUMS
Checksum for /root/.cpan/sources/authors/id/V/VI/VIPUL/Crypt-RSA-1.25.
+tar.gz ok
Crypt-RSA-1.25/
Crypt-RSA-1.25/t/
Crypt-RSA-1.25/t/03-random_octet.t
Crypt-RSA-1.25/t/10-keygen.t
Crypt-RSA-1.25/t/04-octet_xor.t
Crypt-RSA-1.25/t/08-secretkey.t
Crypt-RSA-1.25/t/00-errorhandler.t
Crypt-RSA-1.25/t/02-os2ip.t
Crypt-RSA-1.25/t/01-i2osp.t
Crypt-RSA-1.25/t/11-wrapper.t
Crypt-RSA-1.25/t/09-publickey.t
Crypt-RSA-1.25/t/06-oaep.t
Crypt-RSA-1.25/t/07-pss.t
Crypt-RSA-1.25/t/05-primitives.t
Crypt-RSA-1.25/lib/
Crypt-RSA-1.25/lib/Crypt/
Crypt-RSA-1.25/lib/Crypt/RSA/
....and so on. I've never installed modules any other way; I suspect that whatever machine you are logging into, doesn't have that module yet(?)