CODEWITHSUNDEEP
c++kotlinaesrijndael
Cracker
Cracker

Reputation: 51

How to decrypt c++ the aes Rijndael CBC using kotlin properly?

Md5 hashed value (salt+password)

hashed: "89d1ed22aac58f5bbea53b2fde81a946" (String)(32 characters)

Original string value

orginal: "test" (String)

Encryption Key & IV (Bytes)

Key: "encryptionkeyhere" (String)

16 bit key: 646C646873766D666C766D000000000 (Bytes)(Converted to 16 Bytes)

16 bit IV: 00000000000000000000000000000000 (Bytes)

Encrypted hex value

084987B6C979950A11EBE33A5499B091D127CD208E95BAE5C6B5DE5FAE65AFB68EB5C083BB808FDFD98C16694E6FCA9F2E15DF5A63FBD7E4E7EFFB242D0D56B1A3C35F76F977A70F5A9A1EAD0FC3A9E61242CBA0AF848FFC5C8C4342F4011E0436D81F6B064E086C802E175F662C43A798ADC38D25684E99E926ED30B900FF89CA66760B7DBDFBF3087378620A69981FB87346512DC6596E7420763C238EC7E2015941F3E613070E737A0D191F4730C3CF70C270B5FA13E44407B7D6D7567B6126241777D80874320B969B8818371CEC91DF97AA42ABE5BCF015D9B17BDC18F2F3E1E7E25794A97C44F760B68F1D24FD96036DFC92AF400D53D1292C1FBDD0296AFE28401D48B2EA486C781B4729E55C8794505C7AC3AB2A35C7B893DE4128A3A59335BC76071E404A9B7D600C19CBB0CB640071C7AF9CB135FC46DD29080707ED30BC9CDA6AE65ACDD84CF52B299408D82333F1A8DBD1F58213671063D7C8C1BB9002563A04BD53B03D802888F299024AD8C9BE2A0749EF920362A4C86129401DB29C2D2A17A960C2038C0DC6CCD18F361A629BBDCA17BFF0EB1EB737AE9F00CAB8CFBE2050749E6F0D6EAB7DC849380E85BC55DA82AF7354D31D8431A47FB385CC5CA01FE1DE064AE3F2426A5135938AD923C4A28661CBDA7F1397326D7921158FB06A2B4A1C6F8D141B2749D8A8B20883A7A168D811057CDA88D595EEC694558C446673B708BABFFB5FA584B2AFE527A9C3B162BD38405FC08250AB5EF1D15C7ED94AB71796A5582E25ADFBF83D7BD146C9BF5FE68FA3ADEA4C0D77A4314D06336F6D503A8C097A0FD54051CDD49ED8ECA34E3150D61C01FBB53208C62D701BEFEB15419776B9FB18437FE2C1B4A9BABFDE3CE83457FF6F3F87F83B9B702450D0409886B9D9490BD665BB1CB3E5E460ACDD7BC51958A3870985D58E4585B

C++ Encryption Code

void CRijndael::Encrypt(char const* in, char* result, size_t n, int iMode)
{
    if(false==m_bKeyInit)
        throw exception(sm_szErrorMsg1);
    //n should be > 0 and multiple of m_blockSize
    if(0==n || n%m_blockSize!=0)
        throw exception(sm_szErrorMsg2);
    int i;
    char const* pin;
    char* presult;
    if(CBC == iMode) //CBC mode, using the Chain
    {
        for(i=0,pin=in,presult=result; i<(int)( n/m_blockSize ); i++)
        {
            Xor(m_chain, pin);
            EncryptBlock(m_chain, presult);
            memcpy(m_chain, presult, m_blockSize);
            pin += m_blockSize;
            presult += m_blockSize;
        }
    }
    else if(CFB == iMode) //CFB mode, using the Chain
    {
        for(i=0,pin=in,presult=result; i<(int)( n/m_blockSize ); i++)
        {
            EncryptBlock(m_chain, presult);
            Xor(presult, pin);
            memcpy(m_chain, presult, m_blockSize);
            pin += m_blockSize;
            presult += m_blockSize;
        }
    }
    else //ECB mode, not using the Chain
    {
        for(i=0,pin=in,presult=result; i<(int)( n/m_blockSize ); i++)
        {
            EncryptBlock(pin, presult);
            pin += m_blockSize;
            presult += m_blockSize;
        }
    }
}

Java/Kotlin Aes Descryption Code

var key = buildKeyFromString(encryptionKey)
val iv = IvParameterSpec(key)
val secretKeySpec = SecretKeySpec(key, "AES")
val cipher = Cipher.getInstance("AES/CBC/NoPadding")
cipher.init(Cipher.DECRYPT_MODE, secretKeySpec, iv)
return cipher.doFinal(encryptedByte)

The problem now is when I decrypt using the kotlin code, the initial string is not encoded properly

Decrypted String value

String: "????58f5bbea53b2fde81a946" (String)(Wrong value)

Decrypted Hex value (32 bytes)

Hex: "5C55005916125F540D170E353866356262656135336232666465383161393436"

Exptected String value

Hashed: "89d1ed22aac58f5bbea53b2fde81a946" (String)(32 characters)

enter image description here

Upvotes: 4

Views: 729

Answers (2)

Cracker
Cracker

Reputation: 51

I have use key variable for both IV and secretkeyspec. So I've changed the IV to 16 bytes 0. 

var key = buildKeyFromString(encryptionKey)
var ivBytes = 16 bytes zero
val iv = IvParameterSpec(ivBytes )
val secretKeySpec = SecretKeySpec(key, "AES")
val cipher = Cipher.getInstance("AES/CBC/NoPadding")
cipher.init(Cipher.DECRYPT_MODE, secretKeySpec, iv)
return cipher.doFinal(encryptedByte)

Upvotes: 0

Topaco
Topaco

Reputation: 49131

The cause of the problem is that different IVs are used for encryption and decryption: The encryption uses a zero vector (0x00000000000000000000000000000000) and the decryption uses the key as IV (0x646C646873766D666C766D0000000000).

By the way, the posted ciphertext is too long. Since the plaintext is 32 bytes in size and no padding is used, the ciphertext is also 32 bytes in size and just corresponds to the first 32 bytes of the posted ciphertext (0x084987B6C979950A11EBE33A5499B091D127CD208E95BAE5C6B5DE5FAE65AFB6).

Upvotes: 2

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