In various login systems, md5 encryption of user passwords is indispensable.
Let's put it this way, even if you see the user's login password through various means, you can't know what it is because of that string of weird things. This is protection.
The md5 encryption operation is irreversible, which means that you cannot calculate its original appearance through that string of weird things.
The following is the complete md5 code. Don't understand the algorithm. Just call it directly when you need it.
Private Const BITS_TO_A_BYTE = 8Private Const BYTES_TO_A_WORD = 4Private Const BITS_TO_A_WORD = 32 Private m_lOnBits(30)Private m_l2Power(30) Private Function LShift(lValue, iShiftBits)If iShiftBits = 0 ThenLShift = lValueExit FunctionElseIf iShiftBits = 31 ThenIf lValue And 1 ThenLShift = &H80000000ElseLShift = 0End IfExit FunctionElseIf iShiftBits < 0 Or iShiftBits > 31 ThenErr.Raise 6End If If (lValue And m_l2Power(31 - iShiftBits)) ThenLShift = ((lValue And m_lOnBits(31 - (iShiftBits + 1))) * m_l2Power(iShiftBits)) Or &H80000000ElseLShift = ((lValue And m_lOnBits(31 - iShiftBits)) * m_l2Power(iShiftBits))End IfEnd Function Private Function RShift(lValue, iShiftBits)If iShiftBits = 0 ThenRShift = If (lValue And &H80000000) ThenRShift = (RShift Or (&H40000000 / m_l2Power(iShiftBits - 1)))End IfEnd Function Private Function RotateLeft(lValue, iShiftBits)RotateLeft = LShift(lValue, iShiftBits) Or RShift(lValue, (32 - iShiftBits) )End Private Function AddUnsigned(lX, lY)Dim lX4Dim lY4Dim lX8Dim lY8Dim lResult lX8 = lX And &H80000000lY8 = lY And &H80000000lX4 = lX And &H40000000lY4 = lY And &H40000000 lResult = (lX And &H3FFFFFF) + (lY And &H3FFFFFFF) If lX4 And lY4 ThenlResult = lResult Xor &H80000000 Xor lX8 Xor lY8ElseIf lX4 Or lY4 ThenIf lResult And &H40000000 ThenlResult = lResult lX8 Xor lY8ElselResult = lResult Xor &H40000000 Xor lX8 Xor lY8End IfElselResult = lResult z)End Function Private Function md5_G(x, y, z)md5_G = (x And z) Or (y And (Not z))End Function Private Function md5_H(x, y, z)md5_H = (x Xor y Xor z )End Function Private Function md5_I(x, y, z)md5_I = (y Xor (x Or (Not z)))End Function Private Sub md5_FF(a, b, c, d, x, s, ac)a = AddUnsigned(a, AddUnsigned(AddUnsigned(md5_F(b, c, d), x), ac))a = RotateLeft(a, s)a = AddUnsigned(a, b)End Sub Private Sub md5_GG(a, b, c, d, x, s, ac)a = AddUnsigned(a, AddUnsigned(AddUnsigned(md5_G(b, c, d), x), ac))a = RotateLeft(a, s)a = AddUnsigned(a, b)End Sub Private Sub md5_HH(a, b, c , d, x, s, ac)a = AddUnsigned(a, AddUnsigned(AddUnsigned(md5_H(b, c, d), x), ac))a = RotateLeft(a, s)a = AddUnsigned(a, b)End Sub Private Sub md5_II(a, b, c, d, x, s, ac)a = AddUnsigned (a, AddUnsigned(AddUnsigned(md5_I(b, c, d), x), ac))a = RotateLeft(a, s)a = AddUnsigned(a, b)End Sub Private Function ConvertToWordArray(sMessage)Dim lMessageLengthDim lNumberOfWordsDim lWordArray()Dim lBytePositionDim lByteCountDim lWordCount Const MODULUS_BITS = 512Const CONGRUENT_BITS = 448 lMessageLength = Len(sMessage) lNumberOfWords = (((lMessageLength + ((MODULUS_BITS - CONGRUENT_BITS) / BITS_TO_A_BYTE)) / (MODULUS_BITS / BITS_TO_A_BYTE)) + 1) * (MODULUS_BITS / BITS_TO_A_WORD)ReDim lWordArray(lNumberOfWords - 1) lBytePosition = 0lByteCount = 0Do Until lByteCount >= lMessageLengthlWordCount = lByteCount / BYTES_TO_A_WORDlBytePosition = (lByteCount Mod BYTES_TO_A_WORD) * BITS_TO_A_BYTElWordArray(lWordCount) = lWordArray(lWordCount) Or LShift(Asc(Mid(sMessage, lByteCount + 1, 1)), lBytePosition)lByteCount = lByteCount + 1Loop lWordCount = lByteCount / BYTES_TO_A_WORDlBytePosition = (lByteCount Mod BYTES_TO_A_WORD) * BITS_TO_A_BYTE lWordArray(lWordCount) = lWordArray(lWordCount) Or LShift(&H80, lBytePosition) lWordArray(lNumberOfWords - 2) = LShift(lMessageLength, 3)lWordArray(lNumberOfWords - 1) = RShift(lMessageLength, 29) ConvertToWordArray = lWordArrayEnd Function Private Function WordToHex(lValue)Dim lByteDim lCount For lCount = 0 To 3lByte = RShift(lValue, lCount * BITS_TO_A_BYTE) And m_lOnBits(BITS_TO_A_BYTE - 1)WordToHex = WordToHex & Right("0" & Hex(lByte), 2)NextEnd Function Public Function MD5(sMessage, stype)m_lOnBits(0) = CLng(1)m_lOnBits(1) = CLng(3)m_lOnBits(2) = CLng(7)m_lOnBits(3) = CLng(15)m_lOnBits(4) = CLng(31)m_lOnBits(5) = CLng(63)m_lOnBits(6) = CLng(127)m_lOnBits(7) = CLng(255)m_lOnBits (8) = CLng(511)m_lOnBits(9) = CLng(1023)m_lOnBits(10) = CLng(2047)m_lOnBits(11) = CLng(4095)m_lOnBits(12) = CLng(8191)m_lOnBits(13) = CLng(16383)m_lOnBits (14) = CLng(32767)m_lOnBits(15) = CLng(65535)m_lOnBits(16) = CLng(131071)m_lOnBits(17) = CLng(262143)m_lOnBits(18) = CLng(524287)m_lOnBits(19) = CLng(1048575)m_lOnBits(20) = CLng(2097151)m_lOnBits(21) = CLng(4194303)m_lOnBits(22) = CLng(8388607)m_lOnBits(23) = CLng(16777215)m_lOnBits(24) = CLng(33554431)m_lOnBits(25) = CLng(67108863)m_lOnBits(26) = CLng(134217727)m_lOnBits(27) = CLng(268435455)m_lOnBits(28) = CLng(536870911)m_lOnBits(29) = CLng(1073741823)m_lOnBits(30) = CLng(2147483647) m_l2Power(0) = CLng(1)m_l2Power(1) = CLng(2)m_l2Power(2) = CLng(4)m_l2Power(3) = CLng(8)m_l2Power(4) = CLng(16)m_l2Power(5) = CLng(32)m_l2Power(6) = CLng(64)m_l2Power(7) = CLng(128)m_l2Power (8) = CLng(256)m_l2Power(9) = CLng(512)m_l2Power(10) = CLng(1024)m_l2Power(11) = CLng(2048)m_l2Power(12) = CLng(4096)m_l2Power(13) = CLng(8192)m_l2Power(14) = CLng(16384)m_l2Power (15) = CLng(32768)m_l2Power(16) = CLng(65536)m_l2Power(17) = CLng(131072)m_l2Power(18) = CLng(262144)m_l2Power(19) = CLng(524288)m_l2Power(20) = CLng(1048576)m_l2Power(21) = CLng(2097152)m_l2Power(22) = CLng(4194304)m_l2Power(23) = CLng(8388608)m_l2Power(24) = CLng(16777216)m_l2Power(25) = CLng(33554432)m_l2Power(26) = CLng(67108864)m_l2Power(27) = CLng(134217728)m_l2Power(28) = CLng(268435456)m_l2Power(29) = CLng(536870912)m_l2Power(30) = CLng(1073741824) Dim S31 = 4Const S32 = 11Const S33 = 16Const S34 = 23Const S41 = 6Const S42 = 10Const S43 = 15Const S44 = 21 x = ConvertToWordArray(sMessage) a = &H67452301b = &HEFCDAB89c = &H98BADCFEd = &H10325476 For k = 0 To UBound(x) Step 16AA = aBB = bCC = cDD = d md5_FF a, b, c, d, x(k + 0), S11, &HD76AA478md5_FF d, a, b, c, x(k + 1), S12, &HE8C7B756md5_FF c, d, a, b, x(k + 2), S13, &H242070DBmd5_FF b, c, d, a, x(k + 3), S14, &HC1BDCEEEmd5_FF a, b, c, d, x(k + 4), S11, &HF57C0FAFmd5_FF d, a, b, c, x(k + 5), S12, &H4787C62Amd5_FF c, d, a, b, x(k + 6), S13, &HA8304613md5_FF b, c, d, a, x(k + 7), S14, &HFD469501md5_FF a, b, c, d, x(k + 8 ), S11, &H698098D8md5_FF d, a, b, c, x(k + 9), S12, &H8B44F7AFmd5_FF c, d, a, b, x(k + 10), S13, &HFFFF5BB1md5_FF b, c, d, a, x(k + 11 ), S14, &H895CD7BEmd5_FF a, b, c, d, x(k + 12), S11, &H6B901122md5_FF d, a, b, c, x(k + 13), S12, &HFD987193md5_FF c, d, a, b, x(k + 14 ), S13, &HA679438Emd5_FF b, c, d, a, x(k + 15), S14, &H49B40821 md5_GG a, b, c, d, x(k + 1), S21, &HF61E2562md5_GG d, a, b, c, x(k + 6), S22, &HC040B340md5_GG c, d, a, b, x(k + 11), S23, &H265E5A51md5_GG b, c, d, a, x(k + 0), S24, &HE9B6C7AAmd5_GG a, b, c, d, x(k + 5 ), S21, &HD62F105Dmd5_GG d, a, b, c, x(k + 10), S22, &H2441453md5_GG c, d, a, b, x(k + 15), S23, &HD8A1E681md5_GG b, c, d, a, x(k + 4 ), S24, &HE7D3FBC8md5_GG a, b, c, d, x(k + 9), S21, &H21E1CDE6md5_GG d, a, b, c, x(k + 14), S22, &HC33707D6md5_GG c, d, a, b, x(k + 3 ), S23, &HF4D50D87md5_GG b, c, d, a, x(k + 8), S24, &H455A14EDmd5_GG a, b, c, d, x(k + 13), S21, &HA9E3E905md5_GG d, a, b, c, x(k + 2 ), S22, &HFCEFA3F8md5_GG c, d, a, b, x(k + 7), S23, &H676F02D9md5_GG b, c, d, a, x(k + 12), S24, &H8D2A4C8A md5_HH a, b, c, d, x(k + 5 ), S31, &HFFFA3942md5_HH d, a, b, c, x(k + 8), S32, &H8771F681md5_HH c, d, a, b, x(k + 11), S33, &H6D9D6122md5_HH b, c, d, a, x(k + 14), S34, &HFDE5380Cmd5_HH a, b, c, d, x(k + 1), S31, &HA4BEEA44md5_HH d, a, b, c, x(k + 4), S32, &H4BDECFA9md5_HH c, d, a, b, x(k + 7), S33, &HF6BB4B60md5_HH b, c, d, a, x(k + 10), S34, &HBEBFBC70md5_HH a, b, c, d, x(k + 13), S31, &H289B7EC6md5_HH d, a, b, c, x(k + 0), S32, &HEAA127FAmd5_HH c, d, a, b, x(k + 3) , S33, &HD4EF3085md5_HH b, c, d, a, x(k + 6), S34, &H4881D05md5_HH a, b, c, d, x(k + 9), S31, &HD9D4D039md5_HH d, a, b, c, x(k + 12), S32, &HE6DB99E5md5_HH c, d, a, b, x(k + 15), S33, &H1FA27CF8md5_HH b, c, d, a, x(k + 2), S34, &HC4AC5665 md5_II a, b, c, d, x(k + 0), S41, &HF4292244md5_II d, a, b, c, x(k + 7), S42, &H432AFF97md5_II c, d, a, b, x(k + 14), S43, &HAB9423A7md5_II b, c, d, a, x(k + 5), S44, &HFC93A039md5_II a, b, c, d, x(k + 12) , S41, &H655B59C3md5_II d, a, b, c, x(k + 3), S42, &H8F0CCC92md5_II c, d, a, b, x(k + 10), S43, &HFFEFF47Dmd5_II b, c, d, a, x(k + 1), S44, &H85845DD1md5_II a, b, c, d, x(k + 8), S41, &H6FA87E4Fmd5_II d, a, b, c, x(k + 15), S42, &HFE2CE6E0md5_II c, d, a, b, x(k + 6), S43, &HA3014314md5_II b, c, d, a, x(k + 13 ), S44, &H4E0811A1md5_II a, b, c, d, x(k + 4), S41, &HF7537E82md5_II d, a, b, c, x(k + 11), S42, &HBD3AF235md5_II c, d, a, b, x(k + 2 ), S43, &H2AD7D2BBmd5_II b, c, d, a, x(k + 9), S44, &HEB86D391 a = AddUnsigned(a, AA)b = AddUnsigned(b, BB)c = AddUnsigned(c, CC)d = AddUnsigned(d, DD )Next If stype = 32 ThenMD5 = LCase(WordToHex(a) & WordToHex(b) & WordToHex(c) & WordToHex(d))ElseMD5 = LCase(WordToHex(b) & WordToHex(c))End IfEnd FunctionSub test()MsgBox MD5("a", 16) '16-bit encrypted MsgBox MD5 ("a", 32) '32-bit encryptionEnd Sub