How to check whether a string is Base64 encoded or not

Question

I want to decode a Base64 encoded string  then store it in my database  If the input is not Base64 encoded  I need to throw an error   How can I check if a string is Base64 encoded

User · Answer

This works in Python   def is base64 string       if len string    4    0 and re test    A-Za-z0-9       Z   string           return True      else          return False

User · Answer

A-Za-z0-9     4     A-Za-z0-9     4   A-Za-z0-9     3    A-Za-z0-9     2         this regular expression helped me identify the base64 in my application in rails  I only had one problem  it is that it recognizes the string  errorDescripcion   I generate an error  to solve it just validate the length of a string

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This snippet may be useful when you know the length of the original content  e g  a checksum   It checks that encoded form has the correct length   public static boolean isValidBase64  final int initialLength  final String string       final int padding     final String regexEnd     switch    initialLength     3         case 1         padding   2         regexEnd                break       case 2         padding   1         regexEnd               break       default         padding   0         regexEnd              final int encodedLength         initialLength   3       padding  gt  0   1   0       4       final String regex     a-zA-Z0-9            encodedLength - padding           regexEnd     return Pattern compile  regex   matcher  string   matches

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There is no way to distinct string and base64 encoded  except the string in your system has some specific limitation or identification

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This works in Python   import base64  def IsBase64 str       try          base64 b64decode str          return True     except Exception as e          return False  if IsBase64  ABC        print  ABC is Base64-encoded and its result after decoding is      str base64 b64decode  ABC    replace  b        replace           else      print  ABC is NOT Base64-encoded     if IsBase64  QUJD        print  QUJD is Base64-encoded and its result after decoding is      str base64 b64decode  QUJD    replace  b        replace           else      print  QUJD is NOT Base64-encoded      Summary  IsBase64  string here   returns true if string here is Base64-encoded  and it returns false if string here was NOT Base64-encoded

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There are many variants of Base64  so consider just determining if your string resembles the varient you expect to handle  As such  you may need to adjust the regex below with respect to the index and padding characters  i e             class String   def resembles base64      self length   4    0  amp  amp  self       A-Za-z0-9       Z    end end   Usage   raise  the string does not resemble Base64  unless my string resembles base64

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It is impossible to check if a string is base64 encoded or not  It is only possible to validate if that string is of a base64 encoded string format  which would mean that it could be a string produced by base64 encoding  to check that  string could be validated against a regexp or a library could be used  many other answers to this question provide good ways to check this  so I won t go into details     For example  string flow is a valid base64 encoded string  But it is impossible to know if it is just a simple string  an English word flow  or is it base 64 encoded string  Z0

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var base64Rejex         A-Z0-9     4       A-Z0-9     2     A-Z0-9     3    A-Z0-9     4    i  var isBase64Valid   base64Rejex test base64Data      base64Data is the base64 string  if  isBase64Valid           true if base64 formate     console log  It is base64      else          false if not in base64 formate     console log  it is not in base64

User · Answer

You can use the following regular expression to check if a string is base64 encoded or not      A-Za-z0-9    4     A-Za-z0-9    3    A-Za-z0-9    2         In base64 encoding  the character set is  A-Z  a-z  0-9  and       If the rest length is less than 4  the string is padded with     characters      A-Za-z0-9    4    means the string starts with 0 or more base64 groups     A-Za-z0-9    4   A-Za-z0-9    3    A-Za-z0-9    2      means the string ends in one of three forms   A-Za-z0-9    4    A-Za-z0-9    3   or  A-Za-z0-9    2

User · Answer

Try this    public void checkForEncode String string        String pattern       A-Za-z0-9    4     A-Za-z0-9    4   A-Za-z0-9    3    A-Za-z0-9    2            Pattern r   Pattern compile pattern       Matcher m   r matcher string       if  m find              System out println  true          else           System out println  false

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Check to see IF the string s length is a multiple of 4  Aftwerwards use this regex to make sure all characters in the string are base64 characters    A a-zA-Z d        2  z  If the library you use adds a newline as a way of observing the 76 max chars per line rule  replace them with empty strings

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Try this using a previously mentioned regex   String regex       A-Za-z0-9    4     A-Za-z0-9    4   A-Za-z0-9    3    A-Za-z0-9    2        if  TXkgdGVzdCBzdHJpbmc   matches regex        System out println  it s a Base64           We can also make a simple validation like  if it has spaces it cannot be Base64   String myString    Hello World    if myString contains           System out println  Not B64      else      System out println  Could be B64 encoded  since it has no spaces

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C   This is performing great              static readonly Regex  base64RegexPattern   new Regex BASE64 REGEX STRING  RegexOptions Compiled    private const String BASE64 REGEX STRING       a-zA-Z0-9       0 3      private static bool IsBase64 this String base64String        var rs     string IsNullOrEmpty base64String   amp  amp   string IsNullOrWhiteSpace base64String   amp  amp  base64String Length    0  amp  amp  base64String Length   4    0  amp  amp   base64String Contains       amp  amp   base64String Contains   t    amp  amp   base64String Contains   r    amp  amp   base64String Contains   n     amp  amp   base64String Length   4    0  amp  amp   base64RegexPattern Match base64String  0  Success       return rs

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If you are using Java  you can actually use commons-codec library import org apache commons codec binary Base64   String stringToBeChecked    quot     quot   boolean isBase64   Base64 isArrayByteBase64 stringToBeChecked getBytes       UPDATE 1  Deprecation Notice Use instead  Base64 isBase64 value                  Tests a given byte array to see if it contains only valid characters within the Base64 alphabet  Currently the        method treats whitespace as valid                 param arrayOctet                   byte array to test         return   code true  if all bytes are valid characters in the Base64 alphabet or if the byte array is empty                   code false   otherwise         deprecated 1 5 Use   link  isBase64 byte      will be removed in 2 0               Deprecated     public static boolean isArrayByteBase64 final byte   arrayOctet            return isBase64 arrayOctet

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if when decoding we get a string with ASCII characters  then the string was   not encoded    RoR  ruby solution   def encoded  str    Base64 decode64 str downcase  scan      ascii      count zero  end  def decoded  str    Base64 decode64 str downcase  scan      ascii      count  gt  0 end

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As of Java 8  you can simply use java util Base64 to try and decode the string   String someString          Base64 Decoder decoder   Base64 getDecoder     try       decoder decode someString     catch IllegalArgumentException iae           That string wasn t valid

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Well you can    Check that the length is a multiple of 4 characters Check that every character is in the set A-Z  a-z  0-9       except for padding at the end which is 0  1 or 2     characters   If you re expecting that it will be base64  then you can probably just use whatever library is available on your platform to try to decode it to a byte array  throwing an exception if it s not valid base 64  That depends on your platform  of course

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I try to use this  yes this one it s working     A-Za-z0-9    4     A-Za-z0-9    3    A-Za-z0-9    2         but I added on the condition to check at least the end of the character is    string lastIndexOf       gt   0

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Try like this for PHP5    where  json is some data that can be base64 encoded  json some data     this will check whether data is base64 encoded or not if  base64 decode  json  true     true                 echo  base64 encoded               else       echo  not base64 encoded        Use this for PHP7      string parameter can be base64 encoded or not  function is base64 encoded  string      this will check if  string is base64 encoded and return true  if it is   if  base64 decode  string  true      false                return true            else     return false

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If the RegEx does not work and you know the format style of the original string  you can reverse the logic  by regexing for this format   For example I work with base64 encoded xml files and just check if the file contains valid xml markup  If it does not I can assume  that it s base64 decoded  This is not very dynamic but works fine for my small application

[base64] How to check whether a string is Base64 encoded or not

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