LRC的效驗(yàn)碼的計(jì)算方法

你對(duì)LRC的理解有問(wèn)題啊……

讓客戶滿意是我們工作的目標(biāo)，不斷超越客戶的期望值來(lái)自于我們對(duì)這個(gè)行業(yè)的熱愛(ài)。我們立志把好的技術(shù)通過(guò)有效、簡(jiǎn)單的方式提供給客戶，將通過(guò)不懈努力成為客戶在信息化領(lǐng)域值得信任、有價(jià)值的長(zhǎng)期合作伙伴，公司提供的服務(wù)項(xiàng)目有：域名申請(qǐng)、雅安服務(wù)器托管、營(yíng)銷(xiāo)軟件、網(wǎng)站建設(shè)、昔陽(yáng)網(wǎng)站維護(hù)、網(wǎng)站推廣。

圖二中的有效ASCII字符串為“010300001388”，因此01+03+00+00+13+88 = 9F，9F的補(bǔ)碼為61，因此校驗(yàn)碼為“61”，即0x36、0x31。

lrc是什么意思？

LRC是縱向冗余校驗(yàn)。

縱向冗余校驗(yàn)（LRC，Longitudinal Redundancy Check）是通信中常用的一種校驗(yàn)形式?？v向冗余校驗(yàn)(LRC)是一種從縱向通道上的特定比特串產(chǎn)生校驗(yàn)比特的錯(cuò)誤檢測(cè)方法。在行列格式中（例如，在磁帶中），LRC經(jīng)常是與VRC一起使用，這樣就會(huì)為每個(gè)字符校驗(yàn)碼。

優(yōu)勢(shì)：

縱向冗余校驗(yàn)的異或校驗(yàn)和可以簡(jiǎn)單快速的計(jì)算出來(lái)，將一個(gè)數(shù)據(jù)塊的所有數(shù)據(jù)字節(jié)遞歸，經(jīng)過(guò)異或選通后即可產(chǎn)生異或校驗(yàn)和。由于算法簡(jiǎn)單，可以快速簡(jiǎn)單地計(jì)算縱向冗余校驗(yàn)。然而，LRC并不很可靠，多個(gè)錯(cuò)誤可能相互抵消，在一個(gè)數(shù)據(jù)塊內(nèi)字節(jié)順序的互換根本識(shí)別不出來(lái)。

因此LRC主要用于快速校驗(yàn)很小的數(shù)據(jù)塊兒（如32B）。在射頻識(shí)別系統(tǒng)中，由于標(biāo)簽的容量一般較小，每次交易的數(shù)據(jù)量也不大，所以這種算法還是比較適合的。

如何利用VB對(duì)一串?dāng)?shù)據(jù)進(jìn)行LRC校驗(yàn) 希望給出代碼和例子

分二步：

一、建立一個(gè)模塊，復(fù)制下面代碼

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

PROV_RSA_FULL

=

1

Private

Const

CRYPT_NEWKEYSET

=

H8

Private

Const

ALG_CLASS_HASH

=

32768

Private

Const

ALG_TYPE_ANY

=

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

Private

Const

HP_HASHVAL

=

2

Private

Const

HP_HASHSIZE

=

4

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

'

Get

default

provider

context

handle

lRes

=

CryptAcquireContext(hCtx,

vbNullString,

_

vbNullString,

PROV_RSA_FULL,

0)

If

lRes

Then

'

Create

the

hash

lRes

=

CryptCreateHash(hCtx,

Algorithm,

0,

0,

hHash)

If

lRes

Then

'

Hash

the

string

lRes

=

CryptHashData(hHash,

ByVal

Str,

Len(Str),

0)

If

lRes

Then

'

Get

the

hash

lenght

lRes

=

CryptGetHashParam(hHash,

HP_HASHSIZE,

lLen,

4,

0)

If

lRes

Then

'

Initialize

the

buffer

ReDim

abData(0

To

lLen

-

1)

'

Get

the

hash

value

lRes

=

CryptGetHashParam(hHash,

HP_HASHVAL,

abData(0),

lLen,

0)

If

lRes

Then

'

Convert

value

to

hex

string

For

lIdx

=

To

UBound(abData)

HashString

=

HashString

_

Right$("0"

Hex$(abData(lIdx)),

2)

Next

End

If

End

If

End

If

'

Release

the

hash

handle

CryptDestroyHash

hHash

End

If

End

If

'

Release

the

provider

context

CryptReleaseContext

hCtx,

'

Raise

an

error

if

lRes

=

If

lRes

=

Then

Err.Raise

Err.LastDllError

End

Function

二、函數(shù)調(diào)用

msgbox

HashString(Text1.Text)

LRC校驗(yàn)碼是怎么計(jì)算的

當(dāng)選用ASCII模式作字符幀，錯(cuò)誤檢測(cè)域包含兩個(gè)ASCII字符。這是使用LRC（縱向冗長(zhǎng)檢測(cè)）方法對(duì)消息內(nèi)容計(jì)算得出的，不包括開(kāi)始的冒號(hào)符及回車(chē)換行符。LRC字符附加在回車(chē)換行符前面。我理解的是各位ASCII碼對(duì)應(yīng)的字符求和，然后位反，最后加1，轉(zhuǎn)化成對(duì)應(yīng)的字符即為lrc校驗(yàn)碼。

信息“:010300010001”中“010300010001”

的LRC校驗(yàn)碼為“FA”，

01+03+00+01+00+01=06 06位取反碼是F9 再加1是FA

很明顯結(jié)果就是FA啊 求和:0000 0110 取反 +1 = 1111 1010