How to decode a Base64 string

Question

I have a normal string in Powershell that is from a text file containing Base64 text  it is stored in  x  I am trying to decode it as such    z    System Text Encoding   Unicode GetString  System Convert   FromBase64String  x      This works if  x was a Base64 string created in Powershell  but it s not   And this does not work on the  x Base64 string that came from a file   z simply ends up as something like      What am I missing  For example   x could be YmxhaGJsYWg  which is Base64 for blahblah   In a nutshell  YmxhaGJsYWg  is in a text file then put into a string in this Powershell code and I try to decode it but end up with    etc

User · Answer

There are no PowerShell-native commands for Base64 conversion - yet  as of PowerShell  Core  7 1   but adding  dedicated cmdlets has been suggested  For now  direct use of  NET is needed  Important   Base64 encoding is an encoding of binary data using bytes whose values are constrained to a well-defined 64-character subrange of the ASCII character set representing printable characters  devised at a time when sending arbitrary bytes was problematic  especially with the high bit set  byte values  gt  0x7f    Therefore  you must always specify explicitly what character encoding the Base64 bytes do   should represent    Ergo   on converting TO Base64  you must first obtain a byte representation of the string you re trying to encode using the character encoding the consumer of the Base64 string expects   on converting FROM Base64  you must interpret the resultant array of bytes as a string using the same encoding that was used to create the Base64 representation    Examples  Note   The following examples convert to and from UTF-8 encoded strings   To convert to and from UTF-16LE   quot Unicode quot   instead  substitute  Text Encoding   Unicode for  Text Encoding   UTF8   Convert TO Base64  PS gt   Convert   ToBase64String  Text Encoding   UTF8 GetBytes  Mot  rhead    TW90w7ZyaGVhZA    Convert FROM Base64  PS gt   Text Encoding   Utf8 GetString  Convert   FromBase64String  TW90w7ZyaGVhZA      Mot  rhead

User · Answer

Isn t encoding taking the text TO base64 and decoding taking base64 BACK to text  You seem be mixing them up here  When I decode using this online decoder I get   BASE64  blahblah UTF8  nVnV   not the other way around  I can t reproduce it completely in PS though  See sample below   PS  gt   System Text Encoding   UTF8 GetString  System Convert   FromBase64String  blahblah    nV nV   PS  gt   System Convert   ToBase64String  System Text Encoding   UTF8 GetBytes  nVnV    blZuVg     EDIT I believe you re using the wrong encoder for your text  The encoded base64 string is encoded from UTF8 or ASCII  string   PS  gt   System Text Encoding   UTF8 GetString  System Convert   FromBase64String  YmxhaGJsYWg     blahblah  PS  gt   System Text Encoding   Unicode GetString  System Convert   FromBase64String  YmxhaGJsYWg           PS  gt   System Text Encoding   ASCII GetString  System Convert   FromBase64String  YmxhaGJsYWg     blahblah

User · Answer

I had issues with spaces showing in between my output and there was no answer online at all to fix this issue  I literally spend many hours trying to find a solution and found one from playing around with the code to the point that I almost did not even know what I typed in at the time that I got it to work  Here is my fix for the issue   System Text Encoding   UTF8 GetString   System Convert   FromBase64String  base64string

User · Answer

Base64 encoding converts three 8-bit bytes  0-255  into four 6-bit bytes  0-63 aka base64   Each of the four bytes indexes an ASCII string which represents the final output as four 8-bit ASCII characters  The indexed string is typically  A-Za-z0-9    with     used as padding  This is why encoded data is 4 3 longer   Base64 decoding is the inverse process  And as one would expect  the decoded data is 3 4 as long   While base64 encoding can encode plain text  its real benefit is encoding non-printable characters which may be interpreted by transmitting systems as control characters   I suggest the original poster render  z as bytes with each bit having meaning to the application  Rendering non-printable characters as text typically invokes Unicode which produces glyphs based on your system s localization   Base64decode  the answer to life the universe and everything     00101010

User · Answer

This page shows up when you google how to convert to base64  so for completeness    b     System Text Encoding   UTF8 GetBytes  blahblah    System Convert   ToBase64String  b

[powershell] How to decode a Base64 string?

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