DE19704069A1 - Data sequence encoding and decoding method - Google Patents

Abstract

The method involves generating a key by a key generator using a password. The key combined with a text forms a cryptogram. The password is provided in a binary form, divided into bytes, entered into a data field and filled with constants to a predetermined size. Each byte of the data field is combined with a logical XOR function and a code byte is formed. The sum of the binary ones of the code byte and the addition of a constant result in an increase of the substitution position. The increase is added to the previous insertion position and a new insertion position is determined. Bytes are taken from the data field at the insertion position and combined with the previous code byte using XOR function. The manipulated bytes are again inserted at the insertion position and the existing bits are overwritten at this place.

Description

The invention relates to a method for encrypting and decrypting data follow, with the help of a password through a key generator an encryption key is generated, which links this with the plain text Cipher forms.

Such an encryption process is already in the specialist literature under the Generic term "polyalphabetic encryption" known.

The key generator that is important for encryption has the task of one Password of limited length to generate a continuous encryption key. However, in today's methods, it is either very computationally expensive conceives and brakes the encryption or the generated key a short period or even a transparent education law. Such Keys provide a cryptanalyst with easy clues to a cipher break. Furthermore, it is already possible today through specially made Processors all password combinations of some encryption methods in one to test acceptable time.

The invention has for its object to provide a method that with With the help of an entered password and a minimal computing effort generates a continuous encryption key, which has a very high period owns and cannot be traced by an education law.

The object is achieved as described in claim 1. The subclaims indicate advantageous further training.

The individual process steps are shown on the following pages poses.  

Description of the procedure

According to the principle explained below, a data sequence is created using a sequential key encrypted. The key is through one Key generator generated and only depends on the password. Only little Changes in the password have a completely different encryption key according to. All encryption is done at the binary level. The data sequence to be encrypted must therefore be in binary form and in Bytes.

A continuation example is used in the description as an aid. The individual bytes of the encryption key are included in the following text Denoted cipher bytes.

First, the characters of the password are sequentially in decimal numbers, that correspond to the character set, and then converted into dual numbers. Further a data field is defined where each dual digit has its own position number owns. The dual digits of the password are entered in this data field and the data field is then alternately padded with ones and zeros.

Figure 1

Then all consecutive bytes with the logical XOR function linked.

Figure 2

In our example, the dual number 0 0 1 0 0 0 0 1 is calculated and results in Decimal notation, the number 33. This is the character after the ASCII code "!" and forms the first cipher byte.

To be able to calculate further characters, the cipher byte is added several links inserted again in the bit structure of the data field. The The insertion position shifts by one with each subsequent run certain value.

In order to calculate the first insertion position, the dual digits of the encryption byte are viewed as 8 decimal values and added. As a result, only a value from 0 to 8 can appear.
Cipher byte: Decimal: 33 Dual: 0 0 1 0 0 0 0 1
Add the dual digits: 0 + 0 + 1 + 0 + 0 + 0 + 0 + 1 = 2
The first insertion position is therefore the dual position 2.

With these initial calculations, the first cipher byte and the first Insert position calculated. These bills form the basis for now following links which, arranged in a loop, the continuous Generate encryption key and thus all other encryption bytes.

Now 16 bits are read from the insertion position and divided into two bytes.

Figure 3

In this case, the bits read are: 0 1 0 1 1 1 0 1 1 0 0 0 0 1 0 1 As already indicated, these are broken down into two bytes:

Byte 1 = 0 1 0 1 1 1 0 1 _B = 93 _D.
Byte 2 = 1 0 0 0 0 1 0 1 _B = 133 _D.

Then byte 2 is linked to the previous cipher byte via XOR to a new byte 3:

To get another cipher byte, you have to add byte 3 to the Reinsert the data field at the calculated insertion position. Subsequently As shown in Figure 2, you can see all the bytes of the data field one below the other link with XOR and receives a new encryption byte. These many and extremely time-consuming XOR operations in Figure 2 can, however, be avoided Reduce the second round to the three following steps without the result differs.  

For this purpose, the first byte is read from the insertion position, which was previously referred to as byte 1, and linked to byte 3 via XOR.

The resulting byte corresponds to a mask. All ones of the mask indicate that if the area in the bit structure is overwritten with a change in the corresponding bit occurs in byte 3. You can then refer to the previous cipher byte and thus the new cipher byte calculate.

Since in most cases the insertion position is not divisible by 8, i.e. a remainder remains through division, the mask must be rotated to the right by this remainder.

Insert position: 2
2 DIV 8 = 0 remainder = 2

In this case, the mask must be rotated 2 bit positions to the right, which means that the last two bit positions of the mask move to positions 7 and 6.

After this rotation process, the mask is directly linked to the previous encryption byte again via XOR. The new cipher byte is created.

Finally, byte 3 can now be inserted in the bit structure be used.

Figure 4

If the insertion position meets the condition <791 and ≦ 799, then the first dual digits are used normally and those that go beyond 799 are continued at the first digit. This will be illustrated in an arbitrarily chosen example.

Furthermore, byte 3 is used to increase the insertion position after calculated the following scheme.

The binary digits of byte 3 are considered and added as 8 decimal values. As a result, only a value from 0 to 8 can appear.

Byte 3: Decimal: 164 Dual: 1 0 1 0 0 1 0 0
Add the dual digits: 1 + 0 + 1 + 0 + 0 + 1 + 0 + 0 = 3

In our example, the sum of the dual digits of byte 3 results in the decimal number 3. This decimal number plus 7 _D (a constant), added to the last insertion position, results in the new insertion position. Thus, the increase in the insertion position can only be between 7 and 15 digits.

Old insertion position: 2
Calculated increase in the insertion position: 3 + 7 = 10
2+ 10 = 12

The new insertion position is therefore the dual position 12.

If the calculated insertion position fulfills condition <799, then from the calculated number, subtracting the number 800.

Arbitrary example

Old insertion position: 797
Calculated increase in insertion position: 9
797 + 9 = 806
Since there is no 806 insertion position, 800 is subtracted.
806 - 800 = 6
New insertion position: 6

A new cipher byte has now been calculated and a new insertion position. Now you can start again 16 bits from the new insertion position to read, to divide, to link with each other in order to create a new one Cipher byte and to calculate a new insertion position.

This can now be continued indefinitely, with new cipher bytes arise.  

To encrypt a data sequence, each original letter is included linked to a cipher byte via the logical function XOR.

Figure 5

The decryption is based on the same principle as the encryption, only that when deciphering the original letter in Figure 5 by the encrypted letters is replaced.

Claims (6)

1. A method for encrypting and decrypting a data sequence, with the help of a password being generated by a key generator, a cipher key which, together with the plain text, forms the ciphertext, characterized in that the password is in binary form and is divided once in bytes Entered into a data field and this is then filled up to a specified size with a constant, that each byte of the data field is linked to one another with the logical function XOR and a cipher byte is created so that the sum of the binary elements of the cipher byte and the addition of a constant increase the insertion position shows that this increase is added to the previous insertion position and so the new insertion position is determined, that bytes are then removed from the data field at the insertion position and are linked via XOR with the previous encryption byte, that these manipulated bytes are again on the insertion position and overwrite the existing bits at this point. 2. The method according to claim 1, characterized in that in claim 1 described process steps up to the encryption of the entire data follow twice or more in succession. 3. The method according to claim 1 or 2, characterized in that the first resulting cipher bytes are discarded and only cipher bytes from one certain number of runs (calculation depth) for encryption be used. 4. The method according to claim 1 or 2, characterized in that the group the data field and the data sequence are not necessarily in bytes (8 bits) but also z. B. in Word (16 bit) or Double Word (32 bit) can. 5. The method according to one or more of claims 1 to 4, characterized records that the encrypted data sequence over a message link is transmitted. 6. The method according to one or more of claims 1 to 4, characterized records that the encrypted data sequence is not transmitted immediately, son on a recording medium such. B. printing paper or magnetic or optical recording media is recorded.