B4J Question Decrypt AES 128 CBC

darabon · Dec 30, 2022

My data is GE3e8Qhyjk6rPiNuUJpDy/hHaCwcKj13fA9tN+ICYQM=
The data is encrypted with AES 128 CBC with 1234567890123456 key without IV
I cannot decrypt that with online sites
But cannot decrypt that in B4j
My code is:

B4X:

    Dim kg As KeyGenerator
    Dim C As Cipher
    Dim decrypted() As Byte
    Dim BConv As ByteConverter
 
    decrypted = b
 
    Dim Key As String = "1234567890123456" ' this is the same key that encrypted the string that was sent

    kg.Initialize("AES")
    kg.KeyFromBytes(Key.GetBytes("UTF8"))
   
    C.Initialize("AES/CBC/NoPadding") ' not 100% sure on the NoPadding part

    decrypted = C.Decrypt(decrypted, kg.Key, False)

agraham · Dec 30, 2022

It looks like your data is Base64 encoded. You don't show the code you use to initialise 'b' which I assume is the encrypted data.

darabon · Dec 30, 2022

agraham said:
It looks like your data is Base64 encoded. You don't show the code you use to initialise 'b' which I assume is the encrypted data.

b variable is decoded base64 string

darabon · Dec 31, 2022

agraham said:
It looks like your data is Base64 encoded. You don't show the code you use to initialise 'b' which I assume is the encrypted data.

B4X:

Dim s As StringUtils
    Dim b() As Byte = s.DecodeBase64("GE3e8Qhyjk6rPiNuUJpDy/hHaCwcKj13fA9tN+ICYQM=")

agraham · Dec 31, 2022

CBC encryption mode needs an initialisation vector which you don't have so I am doubting your description of how it is encrypted. Try

C.Initialize("AES/ECB/NoPadding")

This does decrypt to a UTF8 string as follows, the first part of which looks plausible.

2114019028,1,ev_]��b�^�.3~@�S�

teddybear · Dec 31, 2022

darabon said:
My data is GE3e8Qhyjk6rPiNuUJpDy/hHaCwcKj13fA9tN+ICYQM=
The data is encrypted with AES 128 CBC with 1234567890123456 key without IV
I cannot decrypt that with online sites
But cannot decrypt that in B4j

The original string is "2114019028,1,ev_", it can be encrypted with AES 128 CBC, padding mode is PKCS5Padding, as agraham said #5, it is not without IV, you need an initialisation vector , it is 16 bytes 0.

B4X:

    Dim kg As KeyGenerator
    Dim C As Cipher
    Dim IV(16) As Byte
    For i = 0 To 15
        IV(i) = 0
    Next
    kg.Initialize("AES")
    kg.KeyFromBytes("1234567890123456".GetBytes("utf8"))
    C.Initialize("AES/CBC/PKCS5Padding")
    C.InitialisationVector = IV
    Dim bc As ByteConverter
    Dim b64 As Base64
    Dim datas() As Byte=b64.DecodeStoB("GE3e8Qhyjk6rPiNuUJpDy/hHaCwcKj13fA9tN+ICYQM=")
    datas = C.Decrypt(datas, kg.Key, True)
    Log(bc.StringFromBytes(datas,"utf8")) '2114019028,1,ev_

It's also encrypted or decrypted by online sites

darabon · Dec 31, 2022

teddybear said:
The original string is "2114019028,1,ev_", it can be encrypted with AES 128 CBC, padding mode is PKCS5Padding, as agraham said #5, it is not without IV, you need an initialisation vector , it is 16 bytes 0.

B4X:

Dim kg As KeyGenerator Dim C As Cipher Dim IV(16) As Byte For i = 0 To 15 IV(i) = 0 Next kg.Initialize("AES") Dim pwd() As Byte="1234567890123456".GetBytes("utf8") kg.KeyFromBytes(pwd) C.Initialize("AES/CBC/PKCS5Padding") C.InitialisationVector = IV Dim bc As ByteConverter Dim b64 As Base64 Dim datas() As Byte=b64.DecodeStoB("GE3e8Qhyjk6rPiNuUJpDy/hHaCwcKj13fA9tN+ICYQM=") datas = C.Decrypt(datas, kg.Key, True) Log(bc.StringFromBytes(datas,"utf8")) '2114019028,1,ev_

It's also encrypted or decrypted by online sites

OMG Thanks
I will test that

B4J Question Decrypt AES 128 CBC

darabon

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agraham

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