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ASCII85 Encoding

Tool to decrypt/encrypt with ASCII 85. ASCII85 (or Base85) is a coding system created by Paul E. Rutter similar to base64 encoding, using 5 ASCII characters to code 4 bytes. ASCII 85 is used in PDF file format for example.

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ASCII85 Encoding -

Tag(s) : Telecom,Character Encoding

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ASCII85 Encoding

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ASCII85 Decoder





Also on dCode: Base64 CodingASCII Code

ASCII85 Encoder




Also on dCode: Base64 CodingASCII Code

Tool to decrypt/encrypt with ASCII 85. ASCII85 (or Base85) is a coding system created by Paul E. Rutter similar to base64 encoding, using 5 ASCII characters to code 4 bytes. ASCII 85 is used in PDF file format for example.

Answers to Questions

How to encrypt using ASCII85 encoding

Encryption uses the binary code of the text (depending of the encoding used: ASCIIhref, Unicodehref, etc.) and split it every 32 bytes (usually 4 characters) and calculates the value in base85href.

Let the message be DCODE = 01000100 01000011 01001111 01000100 01000101 (in ASCIIhref)

01000100010000110100111101000100 (base2) = 1145261892 (base10) and 01000101000000000000000000000000 (base2) = 1157627904 (base10) (filled with 3 null characters = 24 times 0 to get 32 bytes.)

1145261892 (base10) = [21, 79, 73, 64, 27] (base85) and 1157627904 (base10) = [22, 15, 0, 26, 69] (base85)

Each value in base 85href is replace by an ASCIIhref character of code (value+33)

21 => ASCIIhref(54) = 6, 79 => ASCIIhref(112) = p, 76 => ASCIIhref(106) = j etc.

The coded message is 6pja<70 (note : 3 final characters were deleted because of the previously 3 added null characters)

How to decrypt ASCII85 encoding

The decryption needs ASCIIhref text (and his binary code), message is then split into groups of 5 characters, whose ASCIIhref code is subtracted of 33.

Let the message be 6pja<70 split into 6pja< and 70 (if the tuple is not 5-character long, it is filled with u : 70uuu)

6pja< = 54 112 106 97 60 (in ASCIIhref) minus 33 = 21 79 73 64 27

70uuu = 55 48 117 117 117 (in ASCIIhref) minus 33 = 22 15 84 84 84

Every tuple of 5 numbers is then considered as a unique number written in base 85href, and converted in base 2href.

[21, 79, 73, 64, 27] (base85) = 01000100010000110100111101000100 (base2)

[22, 15, 84, 84, 84] (base85) = 01000101000010010101011000000101 (base2)

The plain text is then this binary code encoded with initial encoding (ASCIIhref, Unicodehref, etc.), n last characters are ignored when n characters have been added in initial completion step.

01000100 01000011 01001111 01000100 01000101 (00001001 01010110 00000101) = DCODE (ASCIIhref encoding).

How to recognize an ASCII85 ciphered text?

The message uses only ASCIIhref characters of codes 33 to 117 with sometimes spaces, carriage return, but also characters y and z.

The message begins with <~ and ends with ~> (variant Adobe)

the message begins with xbtoa Begin and ends with xbtoa End (variant BTOA)

What is the Adobe variant?

Adobe ASCII85begins with <~ and ends with ~> and authorize z exception.

What is the 'z' exception?

The character z is used (even if it is not in the character list) to indicate a group of zeros, this trick allow reducing the size of the message. (z is used in Adobe and BTOA variants)

What is the 'y' exception?

The character z is used to indicate a group of spaces. (not compatible with Adobe)

When ASCII85 have been invented?

Around 1990

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Team dCode read all messages and answer them if you leave an email (not published). It is thanks to you that dCode has the best ASCII85 Encoding tool. Thank you.


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