Ravindra BagaleCourses & study guides

33. Cryptography Basics

33.1 Goals and the Big Three: Encoding, Hashing, Encryption

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Cryptography protects four things, often remembered as CIA + non-repudiation:

Goal Meaning Tool
Confidentiality Only the right people can read it Encryption
Integrity Nobody changed it Hashing, MAC
Authentication It really came from who it claims Signatures, certificates, MAC
Non-repudiation The sender cannot deny sending it Digital signatures

Now the trio students mix up:

Encoding Hashing Encryption
Purpose Change format for transport Fingerprint / integrity check Keep data secret
Key needed? No No Yes
Reversible? Yes, by anyone No (one-way) Yes, only with the key
Example Base64, URL encoding SHA-256, bcrypt AES, RSA 
echo -n "Pune123" | base64                 # UHVuZTEyMw==  (encoding – NOT security)
echo "UHVuZTEyMw==" | base64 -d            # anyone can decode it
echo -n "Pune123" | sha256sum              # one-way fingerprint

Ravindra Bagale's Tip

"Password base64 madhe save kela, mhanje encrypt kela" – he interview madhe mhanla tar tithech rejection! Base64 he fakt encoding aahe, kuni hi ek command ne decode karto. Encoding = format, hashing = fingerprint, encryption = key ne kulup. He teen vegle aahet he pakka lakshat theva.

Practice task

Encode your name in Base64 and decode it. Hash the same text with md5sum, sha1sum and sha256sum and note the output length of each. Change one letter and hash again – how much of the hash changed?