在各种登陆系统中，用户密码的md5加密是不可少的。
这么说吧，即使你通过各种手段看到了用户的登陆密码，但那一串古古怪怪的东西你也不可能知道它是什么，这就是保护。
md5加密运算是不可逆的，就是说你不能通过那一串古古怪怪的东西算出它原始的样子。
下面是完整的md5代码，不要去理解算法了，用到时拿去直接调用。
Private Const BITS_TO_A_BYTE = 8 Private Const BYTES_TO_A_WORD = 4 Private Const BITS_TO_A_WORD = 32 Private m_lOnBits(30) Private m_l2Power(30) Private Function LShift(lValue, iShiftBits) If iShiftBits = 0 Then LShift = lValue Exit Function ElseIf iShiftBits = 31 Then If lValue And 1 Then LShift = &H80000000 Else LShift = 0 End If Exit Function ElseIf iShiftBits < 0 Or iShiftBits > 31 Then Err.Raise 6 End If If (lValue And m_l2Power(31 - iShiftBits)) Then LShift = ((lValue And m_lOnBits(31 - (iShiftBits + 1))) * m_l2Power(iShiftBits)) Or &H80000000 Else LShift = ((lValue And m_lOnBits(31 - iShiftBits)) * m_l2Power(iShiftBits)) End If End Function Private Function RShift(lValue, iShiftBits) If iShiftBits = 0 Then RShift = lValue Exit Function ElseIf iShiftBits = 31 Then If lValue And &H80000000 Then RShift = 1 Else RShift = 0 End If Exit Function ElseIf iShiftBits < 0 Or iShiftBits > 31 Then Err.Raise 6 End If RShift = (lValue And &H7FFFFFFE) m_l2Power(iShiftBits) If (lValue And &H80000000) Then RShift = (RShift Or (&H40000000 m_l2Power(iShiftBits - 1))) End If End Function Private Function RotateLeft(lValue, iShiftBits) RotateLeft = LShift(lValue, iShiftBits) Or RShift(lValue, (32 - iShiftBits)) End Function Private Function AddUnsigned(lX, lY) Dim lX4 Dim lY4 Dim lX8 Dim lY8 Dim lResult lX8 = lX And &H80000000 lY8 = lY And &H80000000 lX4 = lX And &H40000000 lY4 = lY And &H40000000 lResult = (lX And &H3FFFFFFF) + (lY And &H3FFFFFFF) If lX4 And lY4 Then lResult = lResult Xor &H80000000 Xor lX8 Xor lY8 ElseIf lX4 Or lY4 Then If lResult And &H40000000 Then lResult = lResult Xor &HC0000000 Xor lX8 Xor lY8 Else lResult = lResult Xor &H40000000 Xor lX8 Xor lY8 End If Else lResult = lResult Xor lX8 Xor lY8 End If AddUnsigned = lResult End Function Private Function md5_F(x, y, z) md5_F = (x And y) Or ((Not x) And 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 lMessageLength Dim lNumberOfWords Dim lWordArray() Dim lBytePosition Dim lByteCount Dim lWordCount Const MODULUS_BITS = 512 Const 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 = 0 lByteCount = 0 Do Until lByteCount >= lMessageLength lWordCount = lByteCount BYTES_TO_A_WORD lBytePosition = (lByteCount Mod BYTES_TO_A_WORD) * BITS_TO_A_BYTE lWordArray(lWordCount) = lWordArray(lWordCount) Or LShift(Asc(Mid(sMessage, lByteCount + 1, 1)), lBytePosition) lByteCount = lByteCount + 1 Loop lWordCount = lByteCount BYTES_TO_A_WORD lBytePosition = (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 = lWordArray End Function Private Function WordToHex(lValue) Dim lByte Dim lCount For lCount = 0 To 3 lByte = RShift(lValue, lCount * BITS_TO_A_BYTE) And m_lOnBits(BITS_TO_A_BYTE - 1) WordToHex = WordToHex & Right("0" & Hex(lByte), 2) Next End 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 x Dim k Dim AA Dim BB Dim CC Dim DD Dim a Dim b Dim c Dim d Const S11 = 7 Const S12 = 12 Const S13 = 17 Const S14 = 22 Const S21 = 5 Const S22 = 9 Const S23 = 14 Const S24 = 20 Const S31 = 4 Const S32 = 11 Const S33 = 16 Const S34 = 23 Const S41 = 6 Const S42 = 10 Const S43 = 15 Const S44 = 21 x = ConvertToWordArray(sMessage) a = &H67452301 b = &HEFCDAB89 c = &H98BADCFE d = &H10325476 For k = 0 To UBound(x) Step 16 AA = a BB = b CC = c DD = d md5_FF a, b, c, d, x(k + 0), S11, &HD76AA478 md5_FF d, a, b, c, x(k + 1), S12, &HE8C7B756 md5_FF c, d, a, b, x(k + 2), S13, &H242070DB md5_FF b, c, d, a, x(k + 3), S14, &HC1BDCEEE md5_FF a, b, c, d, x(k + 4), S11, &HF57C0FAF md5_FF d, a, b, c, x(k + 5), S12, &H4787C62A md5_FF c, d, a, b, x(k + 6), S13, &HA8304613 md5_FF b, c, d, a, x(k + 7), S14, &HFD469501 md5_FF a, b, c, d, x(k + 8), S11, &H698098D8 md5_FF d, a, b, c, x(k + 9), S12, &H8B44F7AF md5_FF c, d, a, b, x(k + 10), S13, &HFFFF5BB1 md5_FF b, c, d, a, x(k + 11), S14, &H895CD7BE md5_FF a, b, c, d, x(k + 12), S11, &H6B901122 md5_FF d, a, b, c, x(k + 13), S12, &HFD987193 md5_FF c, d, a, b, x(k + 14), S13, &HA679438E md5_FF b, c, d, a, x(k + 15), S14, &H49B40821 md5_GG a, b, c, d, x(k + 1), S21, &HF61E2562 md5_GG d, a, b, c, x(k + 6), S22, &HC040B340 md5_GG c, d, a, b, x(k + 11), S23, &H265E5A51 md5_GG b, c, d, a, x(k + 0), S24, &HE9B6C7AA md5_GG a, b, c, d, x(k + 5), S21, &HD62F105D md5_GG d, a, b, c, x(k + 10), S22, &H2441453 md5_GG c, d, a, b, x(k + 15), S23, &HD8A1E681 md5_GG b, c, d, a, x(k + 4), S24, &HE7D3FBC8 md5_GG a, b, c, d, x(k + 9), S21, &H21E1CDE6 md5_GG d, a, b, c, x(k + 14), S22, &HC33707D6 md5_GG c, d, a, b, x(k + 3), S23, &HF4D50D87 md5_GG b, c, d, a, x(k + 8), S24, &H455A14ED md5_GG a, b, c, d, x(k + 13), S21, &HA9E3E905 md5_GG d, a, b, c, x(k + 2), S22, &HFCEFA3F8 md5_GG c, d, a, b, x(k + 7), S23, &H676F02D9 md5_GG b, c, d, a, x(k + 12), S24, &H8D2A4C8A md5_HH a, b, c, d, x(k + 5), S31, &HFFFA3942 md5_HH d, a, b, c, x(k + 8), S32, &H8771F681 md5_HH c, d, a, b, x(k + 11), S33, &H6D9D6122 md5_HH b, c, d, a, x(k + 14), S34, &HFDE5380C md5_HH a, b, c, d, x(k + 1), S31, &HA4BEEA44 md5_HH d, a, b, c, x(k + 4), S32, &H4BDECFA9 md5_HH c, d, a, b, x(k + 7), S33, &HF6BB4B60 md5_HH b, c, d, a, x(k + 10), S34, &HBEBFBC70 md5_HH a, b, c, d, x(k + 13), S31, &H289B7EC6 md5_HH d, a, b, c, x(k + 0), S32, &HEAA127FA md5_HH c, d, a, b, x(k + 3), S33, &HD4EF3085 md5_HH b, c, d, a, x(k + 6), S34, &H4881D05 md5_HH a, b, c, d, x(k + 9), S31, &HD9D4D039 md5_HH d, a, b, c, x(k + 12), S32, &HE6DB99E5 md5_HH c, d, a, b, x(k + 15), S33, &H1FA27CF8 md5_HH b, c, d, a, x(k + 2), S34, &HC4AC5665 md5_II a, b, c, d, x(k + 0), S41, &HF4292244 md5_II d, a, b, c, x(k + 7), S42, &H432AFF97 md5_II c, d, a, b, x(k + 14), S43, &HAB9423A7 md5_II b, c, d, a, x(k + 5), S44, &HFC93A039 md5_II a, b, c, d, x(k + 12), S41, &H655B59C3 md5_II d, a, b, c, x(k + 3), S42, &H8F0CCC92 md5_II c, d, a, b, x(k + 10), S43, &HFFEFF47D md5_II b, c, d, a, x(k + 1), S44, &H85845DD1 md5_II a, b, c, d, x(k + 8), S41, &H6FA87E4F md5_II d, a, b, c, x(k + 15), S42, &HFE2CE6E0 md5_II c, d, a, b, x(k + 6), S43, &HA3014314 md5_II b, c, d, a, x(k + 13), S44, &H4E0811A1 md5_II a, b, c, d, x(k + 4), S41, &HF7537E82 md5_II d, a, b, c, x(k + 11), S42, &HBD3AF235 md5_II c, d, a, b, x(k + 2), S43, &H2AD7D2BB md5_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 Then MD5 = LCase(WordToHex(a) & WordToHex(b) & WordToHex(c) & WordToHex(d)) Else MD5 = LCase(WordToHex(b) & WordToHex(c)) End If End Function Sub test() MsgBox MD5("a", 16) '16位加密 MsgBox MD5("a", 32) '32位加密 End Sub
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