function y = base64decode(x) %BASE64DECODE Perform base64 decoding on a string. % % BASE64DECODE(STR) decodes the given base64 string STR. % % Any character not part of the 65-character base64 subset set is silently % ignored. Characters occuring after a '=' padding character are never % decoded. % % STR doesn't have to be a string. The only requirement is that it is a % vector containing values in the range 0-255. % % If the length of the string to decode (after ignoring non-base64 chars) is % not a multiple of 4, then a warning is generated. % % This function is used to decode strings from the Base64 encoding specified % in RFC 2045 - MIME (Multipurpose Internet Mail Extensions). The Base64 % encoding is designed to represent arbitrary sequences of octets in a form % that need not be humanly readable. A 65-character subset ([A-Za-z0-9+/=]) % of US-ASCII is used, enabling 6 bits to be represented per printable % character. % % See also BASE64ENCODE. % Author: Peter John Acklam % Time-stamp: 2004-09-20 08:20:50 +0200 % E-mail: pjacklam@online.no % URL: http://home.online.no/~pjacklam % check number of input arguments error(nargchk(1, 1, nargin)); % remove non-base64 chars x = x ( ( 'A' <= x & x <= 'Z' ) ... | ( 'a' <= x & x <= 'z' ) ... | ( '0' <= x & x <= '9' ) ... | ( x == '+' ) | ( x == '=' ) | ( x == '/' ) ); if rem(length(x), 4) warning('Length of base64 data not a multiple of 4; padding input.'); end k = find(x == '='); if ~isempty(k) x = x(1:k(1)-1); end %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % Now perform the following mapping % % A-Z -> 0 - 25 % a-z -> 26 - 51 % 0-9 -> 52 - 61 % + -> 62 % / -> 63 y = repmat(uint8(0), size(x)); i = 'A' <= x & x <= 'Z'; y(i) = - 'A' + x(i); i = 'a' <= x & x <= 'z'; y(i) = 26 - 'a' + x(i); i = '0' <= x & x <= '9'; y(i) = 52 - '0' + x(i); i = x == '+'; y(i) = 62 - '+' + x(i); i = x == '/'; y(i) = 63 - '/' + x(i); x = y; nebytes = length(x); % number of encoded bytes nchunks = ceil(nebytes/4); % number of chunks/groups % add padding if necessary if rem(nebytes, 4) x(end+1 : 4*nchunks) = 0; end x = reshape(uint8(x), 4, nchunks); y = repmat(uint8(0), 3, nchunks); % for the decoded data %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % Rearrange every 4 bytes into 3 bytes % % 00aaaaaa 00bbbbbb 00cccccc 00dddddd % % to form % % aaaaaabb bbbbcccc ccdddddd y(1,:) = bitshift(x(1,:), 2); % 6 highest bits of y(1,:) y(1,:) = bitor(y(1,:), bitshift(x(2,:), -4)); % 2 lowest bits of y(1,:) y(2,:) = bitshift(x(2,:), 4); % 4 highest bits of y(2,:) y(2,:) = bitor(y(2,:), bitshift(x(3,:), -2)); % 4 lowest bits of y(2,:) y(3,:) = bitshift(x(3,:), 6); % 2 highest bits of y(3,:) y(3,:) = bitor(y(3,:), x(4,:)); % 6 lowest bits of y(3,:) % remove padding switch rem(nebytes, 4) case 2 y = y(1:end-2); case 3 y = y(1:end-1); end % reshape to a row vector and make it a character array y = char(reshape(y, 1, numel(y)));