我似乎花了太长时间在...但是...

I seem to have spent too long on this but...

您的问题是块大小。 TDCP_rijndael相当于MCRYPT_RIJNDAEL_128（不是_256）。 ciph.Init（...）调用中的'256'值仍然是正确的。除此之外，它看起来很好。也就是说，假设你使用的是ansistrings for key / iv或者你使用的是unicode Delphi。

对于unicode Delphi版本，我倾向于使用TBytes和key [0] / iv [0]。

Your problem is the block size. TDCP_rijndael is equivalent to MCRYPT_RIJNDAEL_128 (not _256). The '256' value in ciph.Init(...) call is still correct though. Other than that it looks pretty much ok. That is, assuming you're using ansistrings for key/iv or you're using non-unicode Delphi.
For unicode Delphi versions I'd be inclined to use TBytes and key[0] / iv[0].

填充可能仍然是一个问题。如果是这样，那么这里是我基于PHP手册页面和一些试验和错误的方法。

Padding may still be an issue. If so, then here's what I've mangled up based on the PHP manual pages and some trial and error.

PHP：

function Encrypt($src, $key, $iv)
{
  $block = mcrypt_get_block_size(MCRYPT_RIJNDAEL_128, 'cbc');
  //echo "Block size: " . $block . "\r\n";
  $pad = $block - (strlen($src) % $block);
  $src .= str_repeat(chr($pad), $pad);  

  $enc = mcrypt_encrypt(MCRYPT_RIJNDAEL_128, $key, $src, MCRYPT_MODE_CBC, $iv);
  $r = base64_encode($enc);
  return $r;
}

function Decrypt($src, $key, $iv)
{
  $enc = base64_decode($src);
  $dec = mcrypt_decrypt(MCRYPT_RIJNDAEL_128, $key, $enc, MCRYPT_MODE_CBC, $iv);

  $block = mcrypt_get_block_size(MCRYPT_RIJNDAEL_128, 'cbc');
  $pad = ord($dec[($len = strlen($dec)) - 1]);
  return substr($dec, 0, strlen($dec) - $pad);
}

Delphi：

function DecryptData(Data: string; AKey: AnsiString; AIv: AnsiString): string;
var
  key, iv, src, dest: TBytes;
  cipher: TDCP_rijndael;
  slen, pad: integer;
begin
  //key := Base64DecodeBytes(TEncoding.UTF8.GetBytes(AKey));
  //iv := Base64DecodeBytes(TEncoding.UTF8.GetBytes(AIv));
  key := TEncoding.ASCII.GetBytes(AKey);
  iv := TEncoding.ASCII.GetBytes(AIv);

  src := Base64DecodeBytes(TEncoding.UTF8.GetBytes(Data));

  cipher := TDCP_rijndael.Create(nil);
  try
    cipher.CipherMode := cmCBC;
    slen := Length(src);
    SetLength(dest, slen);
    cipher.Init(key[0], 256, @iv[0]); // DCP uses key size in BITS not BYTES
    cipher.Decrypt(src[0], dest[0], slen);
    // Remove the padding. Get the numerical value of the last byte and remove
    // that number of bytes
    pad := dest[slen - 1];
    SetLength(dest, slen - pad);

    // Base64 encode it
    result := TEncoding.Default.GetString(dest);
  finally
    cipher.Free;
  end;
end;

function EncryptData(Data: string; AKey: AnsiString; AIv: AnsiString): string;
var
  cipher: TDCP_rijndael;
  key, iv, src, dest, b64: TBytes;
  index, slen, bsize, pad: integer;
begin
  //key := Base64DecodeBytes(TEncoding.UTF8.GetBytes(AKey));
  //iv := Base64DecodeBytes(TEncoding.UTF8.GetBytes(AIv));
  key := TEncoding.ASCII.GetBytes(AKey);
  iv := TEncoding.ASCII.GetBytes(AIv);

  src := TEncoding.UTF8.GetBytes(Data);

  cipher := TDCP_rijndael.Create(nil);
  try
    cipher.CipherMode := cmCBC;
    // Add padding.
    // Resize the Value array to make it a multiple of the block length.
    // If it's already an exact multiple then add a full block of padding.
    slen := Length(src);
    bsize := (cipher.BlockSize div 8);
    pad := bsize - (slen mod bsize);
    Inc(slen, pad);
    SetLength(src, slen);
    for index := pad downto 1 do
    begin
      src[slen - index] := pad;
    end;

    SetLength(dest, slen);
    cipher.Init(key[0], 256, @iv[0]); // DCP uses key size in BITS not BYTES
    cipher.Encrypt(src[0], dest[0], slen);

    b64 := Base64EncodeBytes(dest);
    result := TEncoding.Default.GetString(b64);
  finally
    cipher.Free;
  end;
end;

PHP和Delphi函数现在给我一样的答案。

The PHP and Delphi functions now give me the same answer.

编辑

Base64DecodeBytes是我添加到DCP Base64单元的一些代码：

Base64DecodeBytes was a bit of code I added to the DCP Base64 unit:

function Base64DecodeBytes(Input: TBytes): TBytes;
var
  ilen, rlen: integer;
begin
  ilen := Length(Input);
  SetLength(result, (ilen div 4) * 3);
  rlen := Base64Decode(@Input[0], @result[0], ilen);
  // Adjust the length of the output buffer according to the number of valid
  // b64 characters
  SetLength(result, rlen);
end;