How to encrypt and decrypt Base64

xiaoxiao2021-03-13 187

In fact, the algorithm of Base64 encryption and decryption is not very complicated, first defining 64-bit keys, 64 characters are fixed, but the order can vary with their own design. E.g:

Char [] Basetable = new char [64] {

'A', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'I', 'J', 'K', 'L', 'M ',' N ',' o ',' p ',' q ',' r ',' s', 't', 'u', 'V', 'W', 'X', 'Y', 'Z',

'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'I', 'J', 'K', 'L', 'M ',' n ',' o ',' p ',' q ',' r ',' s', 't', 'u', 'V', 'W', 'X', 'Y', 'z',

'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', ' ', '/'};

Next, when encryption is for each character that needs to be encrypted, converted to one of the above 64 characters by a certain algorithm; and when decrypting, any one of the characters in the 64 characters is referred to in the character. . There are many ways to do every character, here is not introduced. It is important to note that "=" characters, it is very important in the base64 encryption algorithm, it is a role.

The following is the full code:

// ----------------------------- Base64 Class ----------------- ---------------------

/ / -------------------------------------------------------------------------------------------- ---------------------------------

// --- File: CLSBase64

// --- Description: The Class File to Encode String or Decode String in Base Algorith

// --- Author: knight

//--Date:OCT.8, 2005

/ / -------------------------------------------------------------------------------------------- ---------------------------------

// --------------------------- {base64 class} ------------------------------------------------------------------------------------------------------------------------------------------ ---------------------

Using system;

Namespace Base64

{

///

/// Summary Description for Clsbase64.

///

PUBLIC CLASS CLSBASE64 {

Private char [] Source;

PRIVATE CHAR [] Lookuptable;

Private Int Length, Length2, Length3;

PRIVATE INT blockCount;

PRIVATE INT PADDINGCOUNT;

Public CLSBase64 ()

{

// Todo: add constructor logic here

Source = NULL;

Length = Length2 = length3 = 0;

Blockcount = 0;

Paddingcount = 0;

}

///

/// Create Base64 char Array Using Default Base64 Char Array

///

/// Return the new base64 char Array

Private char [] createbase64char (ref char [] createpara)

{

Char [] Basetable = new char [64] {

'A', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'I', 'J', 'K', 'L', 'M ',' N ',' o ',' p ',' q ',' r ',' s', 't', 'u', 'V', 'W', 'X', 'Y', 'Z',

'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'I', 'J', 'K', 'L', 'M ',' n ',' o ',' p ',' q ',' r ',' s', 't', 'u', 'V', 'W', 'X', 'Y', 'z',

'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', ' ', '/'};

const Int create_type = 8;

BYTE BPARAVALUE = 0;

BYTE BTEMP;

For (int i = 0; i

{

Btemp = (Byte) (CreatePara [i]);

Switch (btemp% create_type)

{

Case 1:

// 00000001

Btemp = (Byte) (btemp ^ 0x01);

Break;

Case 2:

// 00000010bTemp = (BYTE) (btemp ^ 0x02);

Break;

Case 3:

// 00000100

Btemp = (Byte) (btemp ^ 0x04);

Break;

Case 4:

// 00001000

Btemp = (Byte) (btemp ^ 0x08);

Break;

Case 5:

// 00010000

Btemp = (Byte) (btemp ^ 0x10);

Break;

Case 6:

// 00100000

Btemp = (Byte) (btemp ^ 0x20);

Break;

Case 7:

// 01000000

Btemp = (Byte) (btemp ^ 0x40);

Break;

DEFAULT:

// 10000000

Btemp = (Byte) (btemp ^ 0x80);

Break;

}

BPARAVALUE = (Byte) (BPaRue ^ Btemp);

}

CHAR chrtemp;

INT NINDEX;

Switch (bparavalue% create_type)

{

Case 1:

// Exechange 0 <-> 1, 2 <-> 3, 4 <-> 5, 6 <-> 7

For (int i = 0; I

{

NINDEX = I * CREATE_TYPE;

Chrtemp = baseteable [NINDEX];

Basetable [NINDEX] = BaseTable [NINDEX 1];

BaseTable [NINDEX 1] = Chrtemp;

Chrtemp = BaseTable [NINDEX 2];

BaseTable [NINDEX 2] = BaseTable [NINDEX 3];

BaseTable [NINDEX 3] = Chrtemp;

Chrtemp = BaseTable [NINDEX 4];

BaseTable [NINDEX 4] = BaseTable [NINDEX 5];

BaseTable [NINDEX 5] = Chrtemp;

Chrtemp = BaseTable [NINDEX 6];

Basetable [NINDEX 6] = BaseTable [NINDEX 7];

BaseTable [NINDEX 7] = Chrtemp;

}

Break;

Case 2:

// Exechange 0 <-> 2, 1 <-> 3, 4 <-> 6, 5 <-> 7

For (int i = 0; I

{

NINDEX = I * CREATE_TYPE;

Chrtemp = baseteable [NINDEX];

BaseTable [Nindex] = BaseTable [NINDEX 2];

BaseTable [NINDEX 2] = Chrtemp;

chrtemp = baseteable [NINDEX 1];

BaseTable [NINDEX 1] = BaseTable [NINDEX 3]; BaseTable [NINDEX 3] = Chrtemp;

Chrtemp = BaseTable [NINDEX 4];

BaseTable [NINDEX 4] = BaseTable [NINDEX 6];

BaseTable [NINDEX 6] = Chrtemp;

Chrtemp = baseteable [NINDEX 5];

BaseTable [NINDEX 5] = BaseTable [NINDEX 7];

BaseTable [NINDEX 7] = Chrtemp;

}

Break;

Case 3:

// Exechange 0 <-> 3, 1 <-> 2, 4 <-> 7, 5 <-> 6

For (int i = 0; I

{

NINDEX = I * CREATE_TYPE;

Chrtemp = baseteable [NINDEX];

BaseTable [NINDEX] = BaseTable [NINDEX 3];

BaseTable [NINDEX 3] = Chrtemp;

chrtemp = baseteable [NINDEX 1];

BaseTable [NINDEX 1] = BaseTable [NINDEX 2];

BaseTable [NINDEX 2] = Chrtemp;

Chrtemp = BaseTable [NINDEX 4];

BaseTable [NINDEX 4] = BaseTable [NINDEX 7];

BaseTable [NINDEX 7] = Chrtemp;

Chrtemp = baseteable [NINDEX 5];

Basetable [NINDEX 5] = BaseTable [NINDEX 6];

BaseTable [NINDEX 6] = Chrtemp;

}

Break;

Case 4:

// mirror exechange

For (int i = 0; I

{

NINDEX = I * CREATE_TYPE;

Chrtemp = baseteable [NINDEX];

Basetable [NINDEX] = BaseTable [NINDEX CREATE_TYPE - 1];

BaseTable [NINDEX CREATE_TYPE - 1] = Chrtemp;

chrtemp = baseteable [NINDEX 1];

BaseTable [NINDEX 1] = BaseTable [NINDEX CREATE_TYPE - 2];

BaseTable [NINDEX CREATE_TYPE - 2] = Chrtemp;

Chrtemp = BaseTable [NINDEX 2];

BaseTable [NINDEX 2] = BaseTable [NINDEX CREATE_TYPE - 3];

BaseTable [NINDEX CREATE_TYPE - 3] = Chrtemp; Chrtemp = BaseTable [NINDEX 3];

BaseTable [NINDEX 3] = BaseTable [NINDEX CREATE_TYPE - 4];

BaseTable [NINDEX CREATE_TYPE - 4] = Chrtemp;

}

Break;

Case 5:

// Exechange 0 <-> 4, 1 <-> 5, 2 <-> 6, 3 <-> 7

For (int i = 0; I

{

NINDEX = I * CREATE_TYPE;

Chrtemp = baseteable [NINDEX];

Basetable [NINDEX] = BaseTable [NINDEX 4];

BaseTable [NINDEX 4] = Chrtemp;

chrtemp = baseteable [NINDEX 1];

BaseTable [NINDEX 1] = BaseTable [NINDEX 5];

BaseTable [NINDEX 5] = Chrtemp;

Chrtemp = BaseTable [NINDEX 2];

BaseTable [NINDEX 2] = BaseTable [NINDEX 6];

BaseTable [NINDEX 6] = Chrtemp;

Chrtemp = BaseTable [NINDEX 3];

Basetable [NINDEX 3] = BaseTable [NINDEX 7];

BaseTable [NINDEX 7] = Chrtemp;

}

Break;

Case 6:

// Exechange 0 <-> 5, 1 <-> 6, 2 <-> 7, 3 <-> 4

For (int i = 0; I

{

NINDEX = I * CREATE_TYPE;

Chrtemp = baseteable [NINDEX];

BaseTable [Nindex] = BaseTable [NINDEX 5];

BaseTable [NINDEX 5] = Chrtemp;

chrtemp = baseteable [NINDEX 1];

BaseTable [NINDEX 1] = BaseTable [NINDEX 6];

BaseTable [NINDEX 6] = Chrtemp;

Chrtemp = BaseTable [NINDEX 2];

BaseTable [NINDEX 2] = BaseTable [NINDEX 7];

BaseTable [NINDEX 7] = Chrtemp;

Chrtemp = BaseTable [NINDEX 3];

BaseTable [Nindex 3] = BaseTable [NINDEX 4];

BaseTable [NINDEX 4] = chrtemp;

Break;

Case 7:

// exechange 0 <-> 6, 1 <-> 7, 2 <-> 4, 3 <-> 5

For (int i = 0; I

{

NINDEX = I * CREATE_TYPE;

Chrtemp = baseteable [NINDEX];

BaseTable [Nindex] = BaseTable [NINDEX 6];

BaseTable [NINDEX 6] = Chrtemp;

chrtemp = baseteable [NINDEX 1];

BaseTable [NINDEX 1] = BaseTable [NINDEX 7];

BaseTable [NINDEX 7] = Chrtemp;

Chrtemp = BaseTable [NINDEX 2];

BaseTable [NINDEX 2] = BaseTable [NINDEX 4];

BaseTable [NINDEX 4] = Chrtemp;

Chrtemp = BaseTable [NINDEX 3];

BaseTable [Nindex 3] = BaseTable [NINDEX 5];

BaseTable [NINDEX 5] = Chrtemp;

}

Break;

DEFAULT:

Break;

}

Return BaseTable;

}

///

/// Encode String At Specific Parameter

///

/// return encoded string

Public char [] getencoded (char []

Para

Byte [] Input)

{

Length = input.length;

IF ((Length% 3) == 0)

{

Paddingcount = 0;

Blockcount = Length / 3;

}

Else

{

Paddingcount = 3- (Length% 3); // NEED TO Add Padding

Blockcount = (Length Paddingcount) / 3;

}

Length2 = Length Paddingcount; // or blockcount * 3

Byte [] Source2;

Source2 = new byte [length2];

// Copy Data over Insert Padding

For (int x = 0; x

{

IF (x

{

Source2 [x] = INPUT [x];

}

Else

{

Source2 [x] = 0;

}

BYTE B1, B2, B3;

Byte Temp, Temp1, Temp2, Temp3, Temp4;

Byte [] buffer = new byte [blockcount * 4]; char [] result = new char [blockcount * 4];

For (int x = 0; x

{

B1 = source2 [x * 3];

B2 = source2 [x * 3 1];

B3 = Source2 [x * 3 2];

TEMP1 = (Byte) ((B1 & 252) >> 2); // first

Temp = (BYTE) ((B1 & 3) << 4);

TEMP2 = (BYTE) ((B2 & 240) >> 4);

Temp2 = Temp; // Second

Temp = (BYTE) ((B2 & 15) << 2);

TEMP3 = (Byte) ((B3 & 192) >> 6);

TEMP3 = Temp; // third

TEMP4 = (Byte) (B3 & 63); // four

Buffer [x * 4] = TEMP1;

Buffer [x * 4 1] = TEMP2;

Buffer [x * 4 2] = TEMP3;

Buffer [x * 4 3] = TEMP4;

}

Lookuptable = CreateBase64char (REF

Para

);

For (int x = 0; x

{

Result [x] = Sixbit2Char (buffer [x]);

}

// Covert Last "a" S to "=", based on Paddingcount

Switch (Paddingcount)

{

Case 0: Break;

Case 1: Result [blockcount * 4-1] = '='; Break;

Case 2: Result [blockcount * 4-1] = '=';

Result [blockcount * 4-2] = '=';

Break;

DEFAULT: BREAK;

}

Return Result;

}

Private char sixbit2char (byte b)

{

IF ((b> = 0) && (b <= 63))

{

Return Lookuptable [(int) B];

}

Else

{

// Should not happen;

Return '';

}

///

/// Decode String Using Specific Parameter

///

/// if decoded successfully, return the decoded; else return null

Public Byte [] getDecoded (char []

Para

CHAR [] Input)

{

INT TEMP = 0;

Source = INPUT;

Length = input.length;

IF ((Length% 4)! = 0) Return null; // the string is not encoded with my base64; // Find how Many Padding There Are

While (INPUT [Length - Temp - 1] == '=' && Temp <3)

{

TEMP ;

}

IF (Temp == 3) Return null; // the string is not encoded with my base64;

Paddingcount = temp;

// Calculate the blockcount;

// Assuming All Whitespace and carriage returns / newline were removed.

Blockcount = Length / 4;

Length2 = blockcount * 3;

Byte [] buffer = new byte [length]; // first conversion result

Byte [] buffer2 = new byte [length2]; // decoded array with Padding

Lookuptable = CreateBase64char (REF

Para

);

FOR (int x = 0; x

{

Buffer [x] = char2sixbit (source [x]);

}

BYTE B, B1, B2, B3;

Byte Temp1, Temp2, Temp3, Temp4

For (int x = 0; x

{

Temp1 = buffer [x * 4];

Temp2 = buffer [x * 4 1];

TEMP3 = Buffer [x * 4 2];

TEMP4 = Buffer [x * 4 3];

B = (byte) (Temp1 << 2);

B1 = (Byte) ((Temp2 & 48) >> 4);

B1 = B;

B = (byte) ((Temp2 & 15) << 4);

B2 = (Byte) ((Temp3 & 60) >> 2);

B2 = B;

B = (Byte) ((Temp3 & 3) << 6);

B3 = TEMP4;

B3 = B;

Buffer2 [x * 3] = B1;

Buffer2 [x * 3 1] = b2;

Buffer2 [x * 3 2] = B3;

}

// Remove Paddings

Length3 = longth2-paddingcount;

Byte [] result = new byte [length3];

FOR (int x = 0; x

{

Result [x] = buffer2 [x];

}

Return Result;

}

Private Byte Char2Sixbit (Char C)

{

IF (c == '=')

Return 0;

Else

{

FOR (int x = 0; x <64; x )

{

IF (Lookuptable [x] == C)

Return (Byte) x;

}

// Should Not Reach Here

Return 0;

}

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