No need to split and then rejoin the string: 

use MIME::Base64 qw( decode_base64 );

( my $orig = decode_base64( $_ ) ) =~ s/(.)(?=(.))/ $1 ^ $2 /seg;

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In reply to Re^2: Base64 and byte arrays by jwkrahn
in thread Base64 and byte arrays by joec_

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