http://www.bouncycastle.org/java.html: The Bouncy Castle Crypto package is a Java implementation of cryptographic algorithms. This jar contains JCE provider and lightweight API for the Bouncy Castle Cryptography APIs for JDK 1.5. 
public class org.bouncycastle.util.encoders.Base64
  minor version: 0
  major version: 59
  flags: flags: (0x0021) ACC_PUBLIC, ACC_SUPER
  this_class: org.bouncycastle.util.encoders.Base64
  super_class: java.lang.Object
{
  private static final org.bouncycastle.util.encoders.Encoder encoder;
    descriptor: Lorg/bouncycastle/util/encoders/Encoder;
    flags: (0x001a) ACC_PRIVATE, ACC_STATIC, ACC_FINAL

  static void <clinit>();
    descriptor: ()V
    flags: (0x0008) ACC_STATIC
    Code:
      stack=2, locals=0, args_size=0
         0: .line 9
            new org.bouncycastle.util.encoders.Base64Encoder
            dup
            invokespecial org.bouncycastle.util.encoders.Base64Encoder.<init>:()V
            putstatic org.bouncycastle.util.encoders.Base64.encoder:Lorg/bouncycastle/util/encoders/Encoder;
            return
      LocalVariableTable:
        Start  End  Slot  Name  Signature

  public void <init>();
    descriptor: ()V
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=1, locals=1, args_size=1
        start local 0 // org.bouncycastle.util.encoders.Base64 this
         0: .line 7
            aload 0 /* this */
            invokespecial java.lang.Object.<init>:()V
            return
        end local 0 // org.bouncycastle.util.encoders.Base64 this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    1     0  this  Lorg/bouncycastle/util/encoders/Base64;

  public static byte[] encode(byte[]);
    descriptor: ([B)[B
    flags: (0x0009) ACC_PUBLIC, ACC_STATIC
    Code:
      stack=5, locals=4, args_size=1
        start local 0 // byte[] data
         0: .line 19
            aload 0 /* data */
            arraylength
            iconst_2
            iadd
            iconst_3
            idiv
            iconst_4
            imul
            istore 1 /* len */
        start local 1 // int len
         1: .line 20
            new java.io.ByteArrayOutputStream
            dup
            iload 1 /* len */
            invokespecial java.io.ByteArrayOutputStream.<init>:(I)V
            astore 2 /* bOut */
        start local 2 // java.io.ByteArrayOutputStream bOut
         2: .line 24
            getstatic org.bouncycastle.util.encoders.Base64.encoder:Lorg/bouncycastle/util/encoders/Encoder;
            aload 0 /* data */
            iconst_0
            aload 0 /* data */
            arraylength
            aload 2 /* bOut */
            invokeinterface org.bouncycastle.util.encoders.Encoder.encode:([BIILjava/io/OutputStream;)I
            pop
         3: .line 25
            goto 6
         4: .line 26
      StackMap locals: byte[] int java.io.ByteArrayOutputStream
      StackMap stack: java.io.IOException
            astore 3 /* e */
        start local 3 // java.io.IOException e
         5: .line 28
            new java.lang.RuntimeException
            dup
            new java.lang.StringBuilder
            dup
            ldc "exception encoding base64 string: "
            invokespecial java.lang.StringBuilder.<init>:(Ljava/lang/String;)V
            aload 3 /* e */
            invokevirtual java.lang.StringBuilder.append:(Ljava/lang/Object;)Ljava/lang/StringBuilder;
            invokevirtual java.lang.StringBuilder.toString:()Ljava/lang/String;
            invokespecial java.lang.RuntimeException.<init>:(Ljava/lang/String;)V
            athrow
        end local 3 // java.io.IOException e
         6: .line 31
      StackMap locals:
      StackMap stack:
            aload 2 /* bOut */
            invokevirtual java.io.ByteArrayOutputStream.toByteArray:()[B
            areturn
        end local 2 // java.io.ByteArrayOutputStream bOut
        end local 1 // int len
        end local 0 // byte[] data
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    7     0  data  [B
            1    7     1   len  I
            2    7     2  bOut  Ljava/io/ByteArrayOutputStream;
            5    6     3     e  Ljava/io/IOException;
      Exception table:
        from    to  target  type
           2     3       4  Class java.io.IOException
    MethodParameters:
      Name  Flags
      data  

  public static int encode(byte[], java.io.OutputStream);
    descriptor: ([BLjava/io/OutputStream;)I
    flags: (0x0009) ACC_PUBLIC, ACC_STATIC
    Code:
      stack=5, locals=2, args_size=2
        start local 0 // byte[] data
        start local 1 // java.io.OutputStream out
         0: .line 44
            getstatic org.bouncycastle.util.encoders.Base64.encoder:Lorg/bouncycastle/util/encoders/Encoder;
            aload 0 /* data */
            iconst_0
            aload 0 /* data */
            arraylength
            aload 1 /* out */
            invokeinterface org.bouncycastle.util.encoders.Encoder.encode:([BIILjava/io/OutputStream;)I
            ireturn
        end local 1 // java.io.OutputStream out
        end local 0 // byte[] data
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    1     0  data  [B
            0    1     1   out  Ljava/io/OutputStream;
    Exceptions:
      throws java.io.IOException
    MethodParameters:
      Name  Flags
      data  
      out   

  public static int encode(byte[], int, int, java.io.OutputStream);
    descriptor: ([BIILjava/io/OutputStream;)I
    flags: (0x0009) ACC_PUBLIC, ACC_STATIC
    Code:
      stack=5, locals=4, args_size=4
        start local 0 // byte[] data
        start local 1 // int off
        start local 2 // int length
        start local 3 // java.io.OutputStream out
         0: .line 59
            getstatic org.bouncycastle.util.encoders.Base64.encoder:Lorg/bouncycastle/util/encoders/Encoder;
            aload 0 /* data */
            iload 1 /* off */
            iload 2 /* length */
            aload 3 /* out */
            invokeinterface org.bouncycastle.util.encoders.Encoder.encode:([BIILjava/io/OutputStream;)I
            ireturn
        end local 3 // java.io.OutputStream out
        end local 2 // int length
        end local 1 // int off
        end local 0 // byte[] data
      LocalVariableTable:
        Start  End  Slot    Name  Signature
            0    1     0    data  [B
            0    1     1     off  I
            0    1     2  length  I
            0    1     3     out  Ljava/io/OutputStream;
    Exceptions:
      throws java.io.IOException
    MethodParameters:
        Name  Flags
      data    
      off     
      length  
      out     

  public static byte[] decode(byte[]);
    descriptor: ([B)[B
    flags: (0x0009) ACC_PUBLIC, ACC_STATIC
    Code:
      stack=5, locals=4, args_size=1
        start local 0 // byte[] data
         0: .line 70
            aload 0 /* data */
            arraylength
            iconst_4
            idiv
            iconst_3
            imul
            istore 1 /* len */
        start local 1 // int len
         1: .line 71
            new java.io.ByteArrayOutputStream
            dup
            iload 1 /* len */
            invokespecial java.io.ByteArrayOutputStream.<init>:(I)V
            astore 2 /* bOut */
        start local 2 // java.io.ByteArrayOutputStream bOut
         2: .line 75
            getstatic org.bouncycastle.util.encoders.Base64.encoder:Lorg/bouncycastle/util/encoders/Encoder;
            aload 0 /* data */
            iconst_0
            aload 0 /* data */
            arraylength
            aload 2 /* bOut */
            invokeinterface org.bouncycastle.util.encoders.Encoder.decode:([BIILjava/io/OutputStream;)I
            pop
         3: .line 76
            goto 6
         4: .line 77
      StackMap locals: byte[] int java.io.ByteArrayOutputStream
      StackMap stack: java.io.IOException
            astore 3 /* e */
        start local 3 // java.io.IOException e
         5: .line 79
            new java.lang.RuntimeException
            dup
            new java.lang.StringBuilder
            dup
            ldc "exception decoding base64 string: "
            invokespecial java.lang.StringBuilder.<init>:(Ljava/lang/String;)V
            aload 3 /* e */
            invokevirtual java.lang.StringBuilder.append:(Ljava/lang/Object;)Ljava/lang/StringBuilder;
            invokevirtual java.lang.StringBuilder.toString:()Ljava/lang/String;
            invokespecial java.lang.RuntimeException.<init>:(Ljava/lang/String;)V
            athrow
        end local 3 // java.io.IOException e
         6: .line 82
      StackMap locals:
      StackMap stack:
            aload 2 /* bOut */
            invokevirtual java.io.ByteArrayOutputStream.toByteArray:()[B
            areturn
        end local 2 // java.io.ByteArrayOutputStream bOut
        end local 1 // int len
        end local 0 // byte[] data
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    7     0  data  [B
            1    7     1   len  I
            2    7     2  bOut  Ljava/io/ByteArrayOutputStream;
            5    6     3     e  Ljava/io/IOException;
      Exception table:
        from    to  target  type
           2     3       4  Class java.io.IOException
    MethodParameters:
      Name  Flags
      data  

  public static byte[] decode(java.lang.String);
    descriptor: (Ljava/lang/String;)[B
    flags: (0x0009) ACC_PUBLIC, ACC_STATIC
    Code:
      stack=5, locals=4, args_size=1
        start local 0 // java.lang.String data
         0: .line 93
            aload 0 /* data */
            invokevirtual java.lang.String.length:()I
            iconst_4
            idiv
            iconst_3
            imul
            istore 1 /* len */
        start local 1 // int len
         1: .line 94
            new java.io.ByteArrayOutputStream
            dup
            iload 1 /* len */
            invokespecial java.io.ByteArrayOutputStream.<init>:(I)V
            astore 2 /* bOut */
        start local 2 // java.io.ByteArrayOutputStream bOut
         2: .line 98
            getstatic org.bouncycastle.util.encoders.Base64.encoder:Lorg/bouncycastle/util/encoders/Encoder;
            aload 0 /* data */
            aload 2 /* bOut */
            invokeinterface org.bouncycastle.util.encoders.Encoder.decode:(Ljava/lang/String;Ljava/io/OutputStream;)I
            pop
         3: .line 99
            goto 6
         4: .line 100
      StackMap locals: java.lang.String int java.io.ByteArrayOutputStream
      StackMap stack: java.io.IOException
            astore 3 /* e */
        start local 3 // java.io.IOException e
         5: .line 102
            new java.lang.RuntimeException
            dup
            new java.lang.StringBuilder
            dup
            ldc "exception decoding base64 string: "
            invokespecial java.lang.StringBuilder.<init>:(Ljava/lang/String;)V
            aload 3 /* e */
            invokevirtual java.lang.StringBuilder.append:(Ljava/lang/Object;)Ljava/lang/StringBuilder;
            invokevirtual java.lang.StringBuilder.toString:()Ljava/lang/String;
            invokespecial java.lang.RuntimeException.<init>:(Ljava/lang/String;)V
            athrow
        end local 3 // java.io.IOException e
         6: .line 105
      StackMap locals:
      StackMap stack:
            aload 2 /* bOut */
            invokevirtual java.io.ByteArrayOutputStream.toByteArray:()[B
            areturn
        end local 2 // java.io.ByteArrayOutputStream bOut
        end local 1 // int len
        end local 0 // java.lang.String data
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    7     0  data  Ljava/lang/String;
            1    7     1   len  I
            2    7     2  bOut  Ljava/io/ByteArrayOutputStream;
            5    6     3     e  Ljava/io/IOException;
      Exception table:
        from    to  target  type
           2     3       4  Class java.io.IOException
    MethodParameters:
      Name  Flags
      data  

  public static int decode(java.lang.String, java.io.OutputStream);
    descriptor: (Ljava/lang/String;Ljava/io/OutputStream;)I
    flags: (0x0009) ACC_PUBLIC, ACC_STATIC
    Code:
      stack=3, locals=2, args_size=2
        start local 0 // java.lang.String data
        start local 1 // java.io.OutputStream out
         0: .line 119
            getstatic org.bouncycastle.util.encoders.Base64.encoder:Lorg/bouncycastle/util/encoders/Encoder;
            aload 0 /* data */
            aload 1 /* out */
            invokeinterface org.bouncycastle.util.encoders.Encoder.decode:(Ljava/lang/String;Ljava/io/OutputStream;)I
            ireturn
        end local 1 // java.io.OutputStream out
        end local 0 // java.lang.String data
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    1     0  data  Ljava/lang/String;
            0    1     1   out  Ljava/io/OutputStream;
    Exceptions:
      throws java.io.IOException
    MethodParameters:
      Name  Flags
      data  
      out   
}
SourceFile: "Base64.java"