VB如何实现文件的校验？
我打算写一个FTP程序上传文件到FTP服务器希望对上传后的文件进行校验
以免出现错误，请问各位大虾，如何实现是对文件进行校验。
听说MD5可以实现能够提供代码？？
[解决办法]
Option Explicit
Private Declare Function CryptAcquireContext Lib "advapi32.dll" Alias "CryptAcquireContextA" (ByRef phProv As Long, ByVal pszContainer As String, ByVal pszProvider As String, ByVal dwProvType As Long, ByVal dwFlags As Long) As Long
Private Declare Function CryptReleaseContext Lib "advapi32.dll" (ByVal hProv As Long, ByVal dwFlags As Long) As Long
Private Declare Function CryptCreateHash Lib "advapi32.dll" (ByVal hProv As Long, ByVal Algid As Long, ByVal hKey As Long, ByVal dwFlags As Long, ByRef phHash As Long) As Long
Private Declare Function CryptDestroyHash Lib "advapi32.dll" (ByVal hHash As Long) As Long
Private Declare Function CryptHashData Lib "advapi32.dll" (ByVal hHash As Long, pbData As Any, ByVal dwDataLen As Long, ByVal dwFlags As Long) As Long
Private Declare Function CryptGetHashParam Lib "advapi32.dll" (ByVal hHash As Long, ByVal dwParam As Long, pbData As Any, pdwDataLen As Long, ByVal dwFlags As Long) As Long
Private Const HP_HASHVAL = 2
Private Const HP_HASHSIZE = 4
Private Const PROV_RSA_FULL = 1
Private Const CRYPT_NEWKEYSET = &H8
Private Const ALG_CLASS_HASH = 32768
Private Const ALG_TYPE_ANY = 0
Private Const ALG_SID_MD2 = 1
Private Const ALG_SID_MD4 = 2
Private Const ALG_SID_MD5 = 3
Private Const ALG_SID_SHA1 = 4
Enum HashAlgorithm
MD2 = ALG_CLASS_HASH Or ALG_TYPE_ANY Or ALG_SID_MD2
MD4 = ALG_CLASS_HASH Or ALG_TYPE_ANY Or ALG_SID_MD4
MD5 = ALG_CLASS_HASH Or ALG_TYPE_ANY Or ALG_SID_MD5
SHA1 = ALG_CLASS_HASH Or ALG_TYPE_ANY Or ALG_SID_SHA1
End Enum
Public Function HashString(ByVal Str As String, Optional ByVal Algorithm As HashAlgorithm = MD5) As String
Dim hCtx As Long
Dim hHash As Long
Dim lRes As Long
Dim lLen As Long
Dim lIdx As Long
Dim abData() As Byte
lRes = CryptAcquireContext(hCtx, vbNullString, vbNullString, PROV_RSA_FULL, 0)
If lRes <> 0 Then
lRes = CryptCreateHash(hCtx, Algorithm, 0, 0, hHash)
If lRes <> 0 Then
lRes = CryptHashData(hHash, ByVal Str, Len(Str), 0)
If lRes <> 0 Then
lRes = CryptGetHashParam(hHash, HP_HASHSIZE, lLen, 4, 0)
If lRes <> 0 Then
ReDim abData(0 To lLen - 1)
lRes = CryptGetHashParam(hHash, HP_HASHVAL, abData(0), lLen, 0)
If lRes <> 0 Then
For lIdx = 0 To UBound(abData)
HashString = HashString & Right$("0" & Hex$(abData(lIdx)), 2)
Next
End If
End If
End If
CryptDestroyHash hHash
End If
End If
CryptReleaseContext hCtx, 0
If lRes = 0 Then Err.Raise Err.LastDllError
End Function
Option Explicit
'Author : Noel A. Dacara (noeldacara@yahoo.com)
'Filename : Checksum CRC32.cls (cCRC32 Class Module)
'Description : Calculate CRC32 Checksum of a file or string
'Date : Tuesday, March 01, 2005, 06:13 PM
'Last Update : Friday, November 25, 2005, 12:18 AM
'You can freely use and distribute this class or upload these codes on any site
'provided that the original credits are kept unmodified.
'Credits goes to:
'Fredrik Qvarfort ?2000, CRC Checksum Class using a precompiled assembler code
'API Declaration
Private Declare Function CallWindowProc Lib "user32" Alias "CallWindowProcA" (ByVal lpPrevWndFunc As Long, ByVal hWnd As Long, ByVal Msg As Long, ByVal wParam As Long, ByVal lParam As Long) As Long
'Variable Declarations
Private m_CRC32Asmbl() As Byte
Private m_CRC32Table(0 To 255) As Long
'//--Procedures--//
Function FileChecksum(File As String) As String
'Returns the CRC32 checksum value of a specified file.
'Make sure the file isn't empty or invalid to avoid errors later
If Len(Dir$(File)) = 0 Then
Exit Function
End If
On Error GoTo Err_Handler
Dim Arr() As Byte
Dim f As Integer
f = FreeFile 'Get any available file number for use
Open File For Binary Access Read As f
'Redimensionized array according to length of file
ReDim Arr(0 To LOF(f) - 1) As Byte
Get #f, , Arr() 'Get file contents
Close #f
'Calculate CRC32 checksum
FileChecksum = Hex$(CalculateBytes(Arr))
Err_Handler:
End Function
Function StringChecksum(Str As String) As String
'Returns the CRC32 checksum value of the specified string.
'Make sure the string has contents before execution to avoid errors
If Not Len(Str) = 0 Then
'Convert into an array of bytes
StringChecksum = Hex$(CalculateBytes(StrConv(Str, vbFromUnicode)))
End If
End Function
'Private Function
Private Function CalculateBytes(Arr() As Byte) As Long
Dim CRC32 As Long
CRC32 = &HFFFFFFFF 'CRC32 must have this default value
'Suppress error if array isn't dimensionized
On Local Error GoTo Err_Handler
Dim i As Long
i = UBound(Arr) - LBound(Arr) + 1 'Precalculate size of array
'Execute the precompiled assembler code to calculate and generate CRC32 checksum value
Call CallWindowProc(VarPtr(m_CRC32Asmbl(0)), VarPtr(CRC32), VarPtr(Arr(LBound(Arr))), VarPtr(m_CRC32Table(0)), i)
Err_Handler:
CalculateBytes = (Not CRC32) 'Return CRC32 value
End Function
Private Sub Class_Initialize()
Dim i As Long
m_CRC32Table(0) = &H0
m_CRC32Table(1) = &H77073096
m_CRC32Table(2) = &HEE0E612C
m_CRC32Table(3) = &H990951BA
m_CRC32Table(4) = &H76DC419
m_CRC32Table(5) = &H706AF48F
m_CRC32Table(6) = &HE963A535
m_CRC32Table(7) = &H9E6495A3
m_CRC32Table(8) = &HEDB8832
m_CRC32Table(9) = &H79DCB8A4
m_CRC32Table(10) = &HE0D5E91E
m_CRC32Table(11) = &H97D2D988
m_CRC32Table(12) = &H9B64C2B
m_CRC32Table(13) = &H7EB17CBD
m_CRC32Table(14) = &HE7B82D07
m_CRC32Table(15) = &H90BF1D91
m_CRC32Table(16) = &H1DB71064
m_CRC32Table(17) = &H6AB020F2
m_CRC32Table(18) = &HF3B97148
m_CRC32Table(19) = &H84BE41DE
m_CRC32Table(20) = &H1ADAD47D
m_CRC32Table(21) = &H6DDDE4EB
m_CRC32Table(22) = &HF4D4B551
m_CRC32Table(23) = &H83D385C7
m_CRC32Table(24) = &H136C9856
m_CRC32Table(25) = &H646BA8C0
m_CRC32Table(26) = &HFD62F97A
m_CRC32Table(27) = &H8A65C9EC
m_CRC32Table(28) = &H14015C4F
m_CRC32Table(29) = &H63066CD9
m_CRC32Table(30) = &HFA0F3D63
m_CRC32Table(31) = &H8D080DF5
m_CRC32Table(32) = &H3B6E20C8
m_CRC32Table(33) = &H4C69105E
m_CRC32Table(34) = &HD56041E4
m_CRC32Table(35) = &HA2677172
m_CRC32Table(36) = &H3C03E4D1
m_CRC32Table(37) = &H4B04D447
m_CRC32Table(38) = &HD20D85FD
m_CRC32Table(39) = &HA50AB56B
m_CRC32Table(40) = &H35B5A8FA
m_CRC32Table(41) = &H42B2986C
m_CRC32Table(42) = &HDBBBC9D6
m_CRC32Table(43) = &HACBCF940
m_CRC32Table(44) = &H32D86CE3
m_CRC32Table(45) = &H45DF5C75
m_CRC32Table(46) = &HDCD60DCF
m_CRC32Table(47) = &HABD13D59
m_CRC32Table(48) = &H26D930AC
m_CRC32Table(49) = &H51DE003A
m_CRC32Table(50) = &HC8D75180
m_CRC32Table(51) = &HBFD06116
m_CRC32Table(52) = &H21B4F4B5
m_CRC32Table(53) = &H56B3C423
m_CRC32Table(54) = &HCFBA9599
m_CRC32Table(55) = &HB8BDA50F
m_CRC32Table(56) = &H2802B89E
m_CRC32Table(57) = &H5F058808
m_CRC32Table(58) = &HC60CD9B2
m_CRC32Table(59) = &HB10BE924
m_CRC32Table(60) = &H2F6F7C87
m_CRC32Table(61) = &H58684C11
m_CRC32Table(62) = &HC1611DAB
m_CRC32Table(63) = &HB6662D3D
m_CRC32Table(64) = &H76DC4190
m_CRC32Table(65) = &H1DB7106
m_CRC32Table(66) = &H98D220BC
m_CRC32Table(67) = &HEFD5102A
m_CRC32Table(68) = &H71B18589
m_CRC32Table(69) = &H6B6B51F
m_CRC32Table(70) = &H9FBFE4A5
m_CRC32Table(71) = &HE8B8D433
m_CRC32Table(72) = &H7807C9A2
m_CRC32Table(73) = &HF00F934
m_CRC32Table(74) = &H9609A88E
m_CRC32Table(75) = &HE10E9818
m_CRC32Table(76) = &H7F6A0DBB
m_CRC32Table(77) = &H86D3D2D
m_CRC32Table(78) = &H91646C97
m_CRC32Table(79) = &HE6635C01
m_CRC32Table(80) = &H6B6B51F4
m_CRC32Table(81) = &H1C6C6162
m_CRC32Table(82) = &H856530D8
m_CRC32Table(83) = &HF262004E
m_CRC32Table(84) = &H6C0695ED
m_CRC32Table(85) = &H1B01A57B
m_CRC32Table(86) = &H8208F4C1
m_CRC32Table(87) = &HF50FC457
m_CRC32Table(88) = &H65B0D9C6
m_CRC32Table(89) = &H12B7E950
m_CRC32Table(90) = &H8BBEB8EA
m_CRC32Table(91) = &HFCB9887C
m_CRC32Table(92) = &H62DD1DDF
m_CRC32Table(93) = &H15DA2D49
m_CRC32Table(94) = &H8CD37CF3
m_CRC32Table(95) = &HFBD44C65
m_CRC32Table(96) = &H4DB26158
m_CRC32Table(97) = &H3AB551CE
m_CRC32Table(98) = &HA3BC0074
m_CRC32Table(99) = &HD4BB30E2
m_CRC32Table(100) = &H4ADFA541
m_CRC32Table(101) = &H3DD895D7
m_CRC32Table(102) = &HA4D1C46D
m_CRC32Table(103) = &HD3D6F4FB
m_CRC32Table(104) = &H4369E96A
m_CRC32Table(105) = &H346ED9FC
m_CRC32Table(106) = &HAD678846
m_CRC32Table(107) = &HDA60B8D0
m_CRC32Table(108) = &H44042D73
m_CRC32Table(109) = &H33031DE5
m_CRC32Table(110) = &HAA0A4C5F
m_CRC32Table(111) = &HDD0D7CC9
m_CRC32Table(112) = &H5005713C
m_CRC32Table(113) = &H270241AA
m_CRC32Table(114) = &HBE0B1010
m_CRC32Table(115) = &HC90C2086
m_CRC32Table(116) = &H5768B525
m_CRC32Table(117) = &H206F85B3
m_CRC32Table(118) = &HB966D409
m_CRC32Table(119) = &HCE61E49F
m_CRC32Table(120) = &H5EDEF90E
m_CRC32Table(121) = &H29D9C998
m_CRC32Table(122) = &HB0D09822
m_CRC32Table(123) = &HC7D7A8B4
m_CRC32Table(124) = &H59B33D17
m_CRC32Table(125) = &H2EB40D81
m_CRC32Table(126) = &HB7BD5C3B
m_CRC32Table(127) = &HC0BA6CAD
m_CRC32Table(128) = &HEDB88320
m_CRC32Table(129) = &H9ABFB3B6
m_CRC32Table(130) = &H3B6E20C
m_CRC32Table(131) = &H74B1D29A
m_CRC32Table(132) = &HEAD54739
m_CRC32Table(133) = &H9DD277AF
m_CRC32Table(134) = &H4DB2615
m_CRC32Table(135) = &H73DC1683
m_CRC32Table(136) = &HE3630B12
m_CRC32Table(137) = &H94643B84
m_CRC32Table(138) = &HD6D6A3E
m_CRC32Table(139) = &H7A6A5AA8
m_CRC32Table(140) = &HE40ECF0B
m_CRC32Table(141) = &H9309FF9D
m_CRC32Table(142) = &HA00AE27
m_CRC32Table(143) = &H7D079EB1
m_CRC32Table(144) = &HF00F9344
m_CRC32Table(145) = &H8708A3D2
m_CRC32Table(146) = &H1E01F268
m_CRC32Table(147) = &H6906C2FE
m_CRC32Table(148) = &HF762575D
m_CRC32Table(149) = &H806567CB
m_CRC32Table(150) = &H196C3671
m_CRC32Table(151) = &H6E6B06E7
m_CRC32Table(152) = &HFED41B76
m_CRC32Table(153) = &H89D32BE0
m_CRC32Table(154) = &H10DA7A5A
m_CRC32Table(155) = &H67DD4ACC
m_CRC32Table(156) = &HF9B9DF6F
m_CRC32Table(157) = &H8EBEEFF9
m_CRC32Table(158) = &H17B7BE43
m_CRC32Table(159) = &H60B08ED5
m_CRC32Table(160) = &HD6D6A3E8
m_CRC32Table(161) = &HA1D1937E
m_CRC32Table(162) = &H38D8C2C4
m_CRC32Table(163) = &H4FDFF252
m_CRC32Table(164) = &HD1BB67F1
m_CRC32Table(165) = &HA6BC5767
m_CRC32Table(166) = &H3FB506DD
m_CRC32Table(167) = &H48B2364B
m_CRC32Table(168) = &HD80D2BDA
m_CRC32Table(169) = &HAF0A1B4C
m_CRC32Table(170) = &H36034AF6
m_CRC32Table(171) = &H41047A60
m_CRC32Table(172) = &HDF60EFC3
m_CRC32Table(173) = &HA867DF55
m_CRC32Table(174) = &H316E8EEF
m_CRC32Table(175) = &H4669BE79
m_CRC32Table(176) = &HCB61B38C
m_CRC32Table(177) = &HBC66831A
m_CRC32Table(178) = &H256FD2A0
m_CRC32Table(179) = &H5268E236
m_CRC32Table(180) = &HCC0C7795
m_CRC32Table(181) = &HBB0B4703
m_CRC32Table(182) = &H220216B9
m_CRC32Table(183) = &H5505262F
m_CRC32Table(184) = &HC5BA3BBE
m_CRC32Table(185) = &HB2BD0B28
m_CRC32Table(186) = &H2BB45A92
m_CRC32Table(187) = &H5CB36A04
m_CRC32Table(188) = &HC2D7FFA7
m_CRC32Table(189) = &HB5D0CF31
m_CRC32Table(190) = &H2CD99E8B
m_CRC32Table(191) = &H5BDEAE1D
m_CRC32Table(192) = &H9B64C2B0
m_CRC32Table(193) = &HEC63F226
m_CRC32Table(194) = &H756AA39C
m_CRC32Table(195) = &H26D930A
m_CRC32Table(196) = &H9C0906A9
m_CRC32Table(197) = &HEB0E363F
m_CRC32Table(198) = &H72076785
m_CRC32Table(199) = &H5005713
m_CRC32Table(200) = &H95BF4A82
m_CRC32Table(201) = &HE2B87A14
m_CRC32Table(202) = &H7BB12BAE
m_CRC32Table(203) = &HCB61B38
m_CRC32Table(204) = &H92D28E9B
m_CRC32Table(205) = &HE5D5BE0D
m_CRC32Table(206) = &H7CDCEFB7
m_CRC32Table(207) = &HBDBDF21
m_CRC32Table(208) = &H86D3D2D4
m_CRC32Table(209) = &HF1D4E242
m_CRC32Table(210) = &H68DDB3F8
m_CRC32Table(211) = &H1FDA836E
m_CRC32Table(212) = &H81BE16CD
m_CRC32Table(213) = &HF6B9265B
m_CRC32Table(214) = &H6FB077E1
m_CRC32Table(215) = &H18B74777
m_CRC32Table(216) = &H88085AE6
m_CRC32Table(217) = &HFF0F6A70
m_CRC32Table(218) = &H66063BCA
m_CRC32Table(219) = &H11010B5C
m_CRC32Table(220) = &H8F659EFF
m_CRC32Table(221) = &HF862AE69
m_CRC32Table(222) = &H616BFFD3
m_CRC32Table(223) = &H166CCF45
m_CRC32Table(224) = &HA00AE278
m_CRC32Table(225) = &HD70DD2EE
m_CRC32Table(226) = &H4E048354
m_CRC32Table(227) = &H3903B3C2
m_CRC32Table(228) = &HA7672661
m_CRC32Table(229) = &HD06016F7
m_CRC32Table(230) = &H4969474D
m_CRC32Table(231) = &H3E6E77DB
m_CRC32Table(232) = &HAED16A4A
m_CRC32Table(233) = &HD9D65ADC
m_CRC32Table(234) = &H40DF0B66
m_CRC32Table(235) = &H37D83BF0
m_CRC32Table(236) = &HA9BCAE53
m_CRC32Table(237) = &HDEBB9EC5
m_CRC32Table(238) = &H47B2CF7F
m_CRC32Table(239) = &H30B5FFE9
m_CRC32Table(240) = &HBDBDF21C
m_CRC32Table(241) = &HCABAC28A
m_CRC32Table(242) = &H53B39330
m_CRC32Table(243) = &H24B4A3A6
m_CRC32Table(244) = &HBAD03605
m_CRC32Table(245) = &HCDD70693
m_CRC32Table(246) = &H54DE5729
m_CRC32Table(247) = &H23D967BF
m_CRC32Table(248) = &HB3667A2E
m_CRC32Table(249) = &HC4614AB8
m_CRC32Table(250) = &H5D681B02
m_CRC32Table(251) = &H2A6F2B94
m_CRC32Table(252) = &HB40BBE37
m_CRC32Table(253) = &HC30C8EA1
m_CRC32Table(254) = &H5A05DF1B
m_CRC32Table(255) = &H2D02EF8D
Const ASM As String = "5589E557565053518B45088B008B750C8B7D108B4D1431DB8A1E30C3C1E80833049F464975F28B4D088901595B585E5F89EC5DC21000"
ReDim m_CRC32Asmbl(0 To Len(ASM) \ 2 - 1) 'Initialize CRC32 precompiled assembly code
For i = 1 To Len(ASM) Step 2
m_CRC32Asmbl(i \ 2) = Val("&H" & Mid$(ASM, i, 2))
Next i
End Sub
那么只要你上过初中，数学不是学的很烂，都会明白，这个很大的原始数据和这个很小的验证数据之间显然不是1-1对应关系。也就是说，存在多个原始数据不同，但是校验数据相同的情况。换一句话说，校验码一致就认为数据传输正确总是存在一定的误判可能性。
要做到100%的精确可能么？答案是不可能，这需要一点数学知识，这里就不证明了。
对于数学家来说，这些校验算法都不可靠，但是对于工程师来说，这些算法还是有差别的，差别在于，MD5、CRC和CheckSum的可靠性关系是依次递减的。
MD5算法显然很好（另外一种算法SHA-1，也是非常常用），因为它具有这么几个性质：（1）很低的碰撞概率，也就是说，碰巧数据传输错误，但是MD5一样的情况，发生的概率无限小，甚至远远比计算机系统的其它部分出故障的概率还低，以至于可以忽略不计。（2）雪崩效应。对数据做一个微小的改变，就会导致MD5值发生完整的变化（3）碰撞算法很难获得，事实上在山大的杨小云破解MD5之前，MD5在工程上被认为是不可逆的算法，这使得你很难恶意根据MD5值去变造、伪造数据（CRC和CheckSum几乎无法抵御恶意的数据篡改），这使得它也被作为数据签名算法。
[解决办法]
MD5 或其他 Hash 算法本身，并不是“数字签名”算法。
所谓 Hash 算法，实际上是取得一个很长的消息的“摘要”。通俗地说，就是抽取特征，来表示文件的唯一性。
用来对摘要执行签名运算的，一般是非对称密码算法。常用的有 RSA 和 ECC（椭圆曲线）算法。持有私钥的签名者的意图，是表示他（她）对文件的认可。
MD5 与 SHA-1, SHA-224, SHA-384, SHA-512 相比，碰撞率是最高的。更何况，杨小云教授发现了它的算法漏洞，可以人为地增高它的碰撞率。更有国外学者再接再厉，找到方法，可以在合理的时间资源下生成一个与原件 MD5 结果相同的伪造的文书。也就是说，可以拿一个伪造的文书来证明你已经数字签名了。目前，在安全要求比较高的场合，MD5 已经被抛弃。美国商用标准，从 2010 年起，就推荐使用 SHA 了。
但实际上，从通讯纠错的角度，MD5 还是绰绰有余，甚至杀鸡牛刀。在通讯领域，一般采用 CRC 校验，不仅简捷快速，而且它的纠错模型是针对通讯中的干扰专门设计的。
[解决办法]
附带说一句，没打算特意纠正楼上。只是，我的工作与密码算法关系密切，平时干的就是这些。
[解决办法]
常规来说，非恶意的安全网络中，通讯底层的校验、重发机制足够保证数据的准确性；再额外校验就显得过量设计了。
如果是有恶意的不安全网络中，那么考虑的应该是数据加密，而不是传送明文。
接收后校验用的最多的是 BT 之类的 P2P 网络：
数据是“明文”的！
众多提供者假定不可信的！
[解决办法]
加密与保证数据的完整性（接收到的文本与预期的一致）无关。即使加密的数据也可能被篡改。
对于保证完整性来说，Hash 是正确的方法。当然，如果对 Hash 结果数字签名就更好了。因为用来比对的 Hash 值也可能是假的。当然，还有一个底线，那就是签名者的公钥是由可信的 CA 签过的。
对明文或密文 Hash 后数字签名，是等价的。
[解决办法]
如果你的程序支持出错重传的话，采用 CRC 校验就足够了。
[解决办法]
如果你不信任文件传输的准确性，又怎么保证校验值的公众性？
两者都在同一条线路上传送。
需求的设定场景是什么？
因何产生校验的需要？
