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Encoding is Not Encryption


It's unfortunate that the words encryption and encoding tend to get used as synonyms. In cryptography they mean two different things.

In short: Encoding is not encryption. Repeat, encoding is not encryption. Strictly speaking, encryption is an encoding operation, but the term encoding is generally used in cryptography to mean that secrecy is not involved.

Encryption

encryption: 1.The process of changing plaintext into ciphertext using a cryptographic algorithm and key. [1]
2. The (reversible) transformation of data by a cryptographic algorithm to produce ciphertext, i.e. to hide the data. [2]

The words encryption and encipherment mean exactly the same thing.

After encryption, the resulting ciphertext should be indistinguishable from random data and it should be virtually impossible to work out the original plaintext without knowing the key (the exact meaning of "impossible" depending on the cryptographic algorithm used and the length of the key).

We generally need to do some encoding of the data both before and after encryption.

Encoding

encode: 1. To convert data by the use of a code. [3]
2. To format (electronic data) according to a standard format. [4]

Encoding covers many different processes, including:

  1. We store textual data encoded in various formats: ASCII, DBCS, EBCDIC, Unicode.
  2. We encode ciphertext and other binary data that cannot be printed (that's the stuff with all the funny characters in it) using various formats: base64, hexadecimal, uuencode, binhex.
  3. We encode our plaintext in a specific format before we encrypt it. We might convert text stored in Unicode into bytes in a certain order and then add padding.
  4. Before using RSA public key encryption or signing, we use an encoding technique on our message (effectively padding plus some control bytes) to make sure the algorithm works properly and to protect against certain known attacks.
  5. We store X.509 certificates in DER-encoded format and in PEM format.
  6. Compressing the data is also referred to as `encoding', which it is.

Don't get confused

To the uninitiated, the result of an encoding operation may make the data look unreadable. Even representing ordinary text in base64 or hexadecimal format can make it harder to read and appear to be stored in a `secret' format. Most people who work in computing can probably recognise hexadecimal encoding of ordinary text. Base64 is much harder. Compressing ordinary text makes it unrecognisable. For example:

hex("Hello, world!")=48656C6C6F2C20776F726C6421
base64("Hello, world!")=SGVsbG8sIHdvcmxkIQ==
Some text before and after compression using the ZLIB algorithm:
000000  68 65 6c 6c 6f 2c 20 68 65 6c 6c 6f 2c 20 68 65  hello, hello, he
000010  6c 6c 6f 2e 20 54 68 69 73 20 69 73 20 61 20 27  llo. This is a '
000020  68 65 6c 6c 6f 20 77 6f 72 6c 64 27 20 6d 65 73  hello world' mes
000030  73 61 67 65 20 66 6f 72 20 74 68 65 20 77 6f 72  sage for the wor
000040  6c 64 2c 20 72 65 70 65 61 74 2c 20 66 6f 72 20  ld, repeat, for 
000050  74 68 65 20 77 6f 72 6c 64 2e                    the world.      
000000  78 9c cb 48 cd c9 c9 d7 51 c8 40 a2 f4 14 42 32  x..H....Q.@...B2
000010  32 8b 15 80 28 51 41 1d 2c a2 50 9e 5f 94 93 a2  2...(QA.,.P._...
000020  ae 90 9b 5a 5c 9c 98 9e aa 90 96 5f a4 50 92 91  ...Z\......_.P..
000030  0a 11 d6 51 28 4a 2d 48 4d 2c d1 41 15 d6 03 00  ...Q(J-HM,.A....
000040  86 d1 1f 4e                                      ...N            

The difference is that there is no security involved. The encoding techniques are not secret. Anyone can carry out the decoding operation. They are not hard to recognize. Be careful.

Further reading

Cryptography with International Character Sets
Cross-Platform Encryption
Using Compression with CryptoSys

References

  1. NIST Special Publication 800-57 DRAFT (April, 2005)
  2. ISO/IEC 10116 (2nd edition): 1997
  3. ATIS Telecom Glossary 2000, T1.523-2001
  4. The American Heritage Dictionary of the English Language, Fourth Edition

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This page last updated 28 August 2010