trigger tokenGenerator on Certification__c (before insert) {
    static string randomString(){
        for(Certification__c c: Trigger.new){
            final String chars = 'BCD';
            String a = '';
            while (a.length() < 1) {
                Integer idx = Math.mod(Math.abs(Crypto.getRandomInteger()), chars.length());
                a += chars.substring(idx, idx+1);
            }
        }
        return a;
    }
    Integer i;
    if(i<100){
        while(c.Name.contains(a)){
            randomString();
            i++;
        }
        c.Name = a;
    }
    else
        c.Name = 'You ran out of TOKENS';
}