Why does a base64 encoded string have an sign at the end

Question

I know what base64 encoding is and how to calculate base64 encoding in C   however I have seen several times that when I convert a string into base64  there is an   at the end   A few questions came up    Does a base64 string always end with    Why does an   get appended at the end

User · Answer

It s padding  From http   en wikipedia org wiki Base64      In theory  the padding character is not needed for decoding  since the   number of missing bytes can be calculated from the number of Base64   digits  In some implementations  the padding character is mandatory    while for others it is not used  One case in which padding characters   are required is concatenating multiple Base64 encoded files

User · Answer

1  No  2  As a short answer  The 65th character   quot   quot  sign  is used only as a complement in the final process of encoding a message  You will not have a     sign if your string has a multiple of 3 characters number  because Base64 encoding takes each three bytes  8 bits  and represents them as four printable characters in the ASCII standard  Details   a  If you want to encode ABCDEFG  lt   gt   ABC   DEF   G Base64 will deal with the first block  producing 4 characters  and the second  as they are complete   But for the third it will add a double    in the output in order to complete the 4 needed characters  Thus  the result will be  QUJD REVG Rw    without spaces    b  If you want to encode ABCDEFGH  lt   gt   ABC   DEF   GH similarly  it will add just a single   in the end of the output to get 4 characters  The result will be  QUJD REVG R0g   without spaces

User · Answer

Its defined in RFC 2045 as a special padding character if fewer than 24 bits are available at the end of the encoded data

User · Answer

It serves as padding   A more complete answer is that a base64 encoded string doesn t always end with a    it will only end with one or two   if they are required to pad the string out to the proper length

User · Answer

http   www hcidata info base64 htm  Encoding  Mary had  to Base 64  In this example we are using a simple text string   Mary had   but the principle holds no matter what the data is  e g  graphics file   To convert each 24 bits of input data to 32 bits of output  Base 64 encoding splits the 24 bits into 4 chunks of 6 bits  The first problem we notice is that  Mary had  is not a multiple of 3 bytes - it is 8 bytes long  Because of this  the last group of bits is only 4 bits long  To remedy this we add two extra bits of  0  and remember this fact by putting a     at the end  If the text string to be converted to Base 64 was 7 bytes long  the last group would have had 2 bits  In this case we would have added four extra bits of  0  and remember this fact by putting      at the end

User · Answer

is a padding character  If the input stream has length that is not a multiple of 3  the padding character will be added  This is required by decoder  if no padding present  the last byte would have an incorrect number of zero bits  Better and deeper explanation here  https   base64tool com detect-whether-provided-string-is-base64-or-not

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From Wikipedia      The final      sequence indicates that the last group contained only one byte  and     indicates that it contained two bytes    Thus  this is some sort of padding

User · Answer

No  To pad the Base64-encoded string to a multiple of 4 characters in length  so that it can be decoded correctly

User · Answer

The equals sign     is used as padding in certain forms of base64 encoding  The Wikipedia article on base64 has all the details

[encoding] Why does a base64 encoded string have an = sign at the end

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