high bit in binary does not affect the low bits in the base64 representation). In converting a binary number to base85 (85 is not a power of two) high bits do affect the low order base85 digits and conversely. Padding the binary low (with zero bits) while encoding and padding the base85 value high (with us) in decoding assures that the high order bits are preserved (the zero padding in the binary gives enough room so that a small addition is trapped and there is no "carry" to the high bits). In Ascii85-encoded blocks, whitespace and line-break characters may be present anywhere, including in the middle of a 5-character block, but they must be silently ignored. Adobe's specification does not support the y exception. Example for Ascii85 A quote from Thomas Hobbes's Leviathan: Man is distinguished, not only by his reason, but by this singular passion from other animals, which is a lust of the mind, that by a perseverance of delight in the continued and indefatigable generation of knowledge, exceeds the short vehemence of any carnal pleasure. If this is initially encoded using US-ASCII, it can be reencoded in Ascii85 as follows: 9jqo^BlbD-BleB1DJ+*+F(f,q/0JhKF<GL>Cj@.4Gp$d7F!,L7@<6@)/0JDEF<G%<+EV:2F!,O< DJ+*.@<*K0@<6L(Df-\0Ec5e;DffZ(EZee.Bl.9pF"AGXBPCsi+DGm>@3BB/F*&OCAfu2/AKYi( DIb:@FD,*)+C]U=@3BN#EcYf8ATD3s@q?d$AftVqCh[NqF<G:8+EV:.+Cf>-FD5W8ARlolDIal( DId<j@<?3r@:F%a+D58'ATD4$Bl@l3De:,-DJs`8ARoFb/0JMK@qB4^F!,R<AKZ&-DfTqBG%G>u D.RTpAKYo'+CT/5+Cei#DII?(E,9)oF*2M7/c Since the last 4-tuple is incomplete, it must be padded with three zero bytes: Since three bytes of padding had to be added, the three final characters 'YkO' are omitted from the output. Decoding is done inversely, except that the last 5-tuple is padded with 'u' characters: Since the input had to be padded with three 'u' bytes, the last three bytes of the output are ignored and we end up with the original period. The input sentence does not contain 4 consecutive zero bytes, so the example does not show the use of the 'z' abbreviation. Compatibility The Ascii85 encoding is compatible with 7-bit and 8-bit MIME, while having less overhead than Base64. One potential compatibility issue of Ascii85 is that some of the characters it uses are significant in markup languages such as XML or SGML. To include ascii85 data in these documents, it may be necessary to escape the quote, angle brackets, and ampersands. RFC 1924 version Published on April 1, 1996, informational : "A Compact Representation of IPv6 Addresses" by Robert Elz suggests a base-85 encoding of IPv6 addresses. This differs from the scheme used above in that he proposes a different set of 85 ASCII characters, and