Cifruri de ascundere
Un cifru nul, cunoscut și sub numele de cifru de ascundere, este o formă veche de criptare în care textul simplu este amestecat cu o cantitate mare de material necifrat. Astăzi este considerată o formă simplă de steganografie, care poate fi folosită pentru a ascunde textul cifrat.
Exemple:
Iată un exemplu de mesaj cifrat, trimis de un german în timpul Primului Război Mondial:
PRESIDENT’S EMBARGO RULING SHOULD HAVE IMMEDIATE NOTICE. GRAVE SITUATION AFFECTING INTERNATIONAL LAW. STATEMENT FORESHADOWS RUIN OF MANY NEUTRALS. YELLOW JOURNALS UNIFYING NATIONAL EXCITEMENT IMMENSELY.
Luarea primei litere a fiecărui cuvânt dezvăluie mesajul ascuns „Pershing sails from N.Y. June I”.
Iată un exemplu mai complicat din Războiul Civil din Anglia, care l-a ajutat pe regalistul Sir John Trevanian în evadarea sa dintr-un castel puritan din Colchester:
WORTHY SIR JOHN, HOPE, THAT IS YE BEST COMFORT OF YE AFFLICTED, CANNOT MUCH, I FEAR ME, HELP YOU NOW. THAT I WOULD SAY TO YOU, IS THIS ONLY: IF EVER I MAY BE ABLE TO REQUITE THAT I DO OWE YOU, STAND NOT UPON ASKING ME. TIS NOT MUCH THAT I CAN DO; BUT WHAT I CAN DO, BEE YE VERY SURE I WILL. I KNOW THAT, IF DEATH COMES, IF ORDINARY MEN FEAR IT, IT FRIGHTS NOT YOU, ACCOUNTING IT FOR A HIGH HONOUR, TO HAVE SUCH A REWARD OF YOUR LOYALTY. PRAY YET YOU MAY BE SPARED THIS SO BITTER, CUP. I FEAR NOT THAT YOU WILL GRUDGE ANY SUFFERINGS; ONLY IF BY SUBMISSIONS YOU CAN TURN THEM AWAY, TIS THE PART OF A WISE MAN. TELL ME, AN IF YOU CAN, TO DO FOR YOU ANYTHING THAT YOU WOULD HAVE DONE. THE GENERAL GOES BACK ON WEDNESDAY. RESTINGE YOUR SERVANT TO COMMAND.
SO TODAY I HEARD FROM UNCLE MOE OVER THE PHONE. HE TOLD ME THAT YOU AND ME GO THE SAME BIRTHDAY. HE SAYS YOUR TIME THERE TESTED YOUR STRENGTH SO STAY POSITIVE AT SUCH TIMES. I’M FOR ALL THAT CLEAN LIVING! METHAMPHETAMINES WAS MY DOWN FALL. THE PROGRAM I’M STARTING THE NINTH IS ONE I HEARD OF A COUPLE WEEKS BEFORE SEPTEMBER THROUGH MY COUNSELOR BARRIOS. BUT MY MEDICAL INSURANCE COVERAGE DENIES THEY COVER IT. I’M USING MY TIME TO CHECK AND IF THE INSURANCE AGENT DENIES STILL MY COVERAGE I’M GETTING TOGETHER PAPERWORK SAYING I TESTED FOR THIS TREATMENT REQUIRED ON THE CHILD CUSTODY. THE NINTH WILL MEAN I HAVE TESTED MY DETERMINATION TO CHANGE. ON THE NEXT FREE WEEKEND THE KIDS ARE COMING, BUT FIRST I GOTTA SHOW CAROLINA I’M STAYING OUT OF TROUBLE WAITING TO GET MYSELF ADMITTED ON THE PROGRAM. THE SUPPORTING PAPERWORK THAT THE FAMILY COURTS GOT WILL ALSO PROVE THERE’S NO REASON NEITHER FOR A WITNESS ON MY CHILDREN’S VISITS. OF COURSE MY BRO HAS HIS MIND MADE UP OF RECENT THAT ALL THIS DRUG USAGE DON’T CONCERN OUR VISITS. I THINK THAT MY KIDS FEEL I NEED THEIR LOVE IF I’M GONNA BE COOL. GUILTY FEELINGS RISE ON ACCOUNT OF THE MISTAKES I COULD WRITEUP. FOR DAYS I’M HERE. HE GOT A GOOD HEART. SHOULD YOU BE HAVING PROBLEMS BE ASSURED THAT WHEN YOU HIT THE STREETS WE’LL BE CONSIDERING YOU…
TESTED ON THE FIRST
I’M WAITING ON PAPERWORK
GOT NO WITNESS OF HIS RECENT USAGE
I FEEL IF GUILTY OF WRITEUP HE SHOULD BE HIT