Electronic watermarking method, electronic information...

Details Electronic watermarking method, electronic information... Electronic watermarking method, electronic information...

1999-01-21

2003-01-28

Darrow, Justin T. (Department: 2132)

Electrical computers and digital processing systems: support

Multiple computer communication using cryptography

Particular communication authentication technique

C713S155000, C713S156000, C713S170000, C705S064000, C705S075000

Reexamination Certificate

active

06513118

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electronic watermarking method, an electronic information distribution system, an image filing apparatus, and a storage medium on which the steps for performing the electronic watermarking method are stored so that they can be read by a computer. In particular, the present invention pertains to an electronic watermarking method for protecting copyrights for digital information, such as moving image data, static image data, audio data, computer data and computer programs, an electronic information distribution system, such as a multimedia network system, for distributing digital information by using the electronic watermarking method, an image filing apparatus that employs the electronic watermarking method, and a storage medium on which steps for performing the electronic watermarking method are stored so that they can be read by a computer.
2. Related Background Art
As a consequence of recent developments concerning computer networks and the availability of inexpensive high-performance computers, electronic transactions for trading in products across a network have become popular. Products for such transactions can be digital data, to include pictures, for example.
However, since a large number of complete copies of digital data can easily be prepared, a user who purchases digital data would be able to illegally prepare copies having the same quality as the original, and could then distribute the copied data. As a result, a warrantable price would not be paid to the owner of the copyright for the digital data or to a person (hereinafter referred to as a “seller”) by whom sale of the digital data is authorized by the copyright owner, and an infringement of the copyright would occur.
Once a copyright holder or a seller (hereinafter a person who legally distributes digital data is generally called a “server”) has transmitted digital data to a user, full protection against the illegal copying of the data is not possible.
Therefore, an electronic watermark technique has been proposed for use instead of a method for the direct prevention of illegal copying. According to the electronic watermark technique, a specific process is performed for the original digital data and copyright information concerning the digital data, or user information, is embedded in the digital data. Thus, when an illegal copy of the digital data is discovered, the person who distributed the copied data can be identified.
In a conventional electronic watermark system, a server is assumed to be fully trustworthy. Therefore, if a server in a conventional system is not trustworthy and should engage in some sort of illegal distribution activity, a user who has committed no crime could be falsely accused of illegally copying data.
This occurs because in a conventional electronic watermark system, as is shown in
FIG. 1
, when a server embeds user information d
1
for identifying a user in digital data g (in the following explanation image data are employed as the digital data), which is distributed to the user, and thereafter, without the permission of the user, makes a further distribution of the data containing the user's identification data, there is no way the user can refute an accusation by the server, even though in this instance it is the server that performed an illegal act.
As a countermeasure, a system (
FIG. 2
) using a public key encryption method has been proposed.
According to the public key encryption method, an encryption key and a decryption key differ, with the encryption key being used as a public key while the decryption key is used as a secret key. RSA encryption and E1Gama1 encryption are typical, well known public key encryption system examples.
An explanation will be given for (a) features of a public key encryption system and (b) protocols for secret communications and authenticated communications.
(a) Features of Public Key Encryption
(1) Since an encryption key and a decryption key differ, and since the encryption key can be published, a secret delivery process is not required for the encryption key and its distribution is easy.
(2) Since the encryption keys of users are published, users need only provide for the secret storage of their decryption keys.
(3) An authentication function can be provided with which a recipient can verify that the sender of a message is not perpetrating a fraud and that the received message has not been altered.
(b) Protocols for Public Key Encryption
For example, when E (kp, M) denotes an encryption operation for a message M that uses a public encryption key kp, and D (ks, M) denotes a decryption operation for a message M that uses a secret decryption key ks, the public key encryption algorithm satisfies the following two conditions.
(1) The calculations for the encryption E (kp, M) can be performed easily using the encryption key kp that is provided, and the calculations for the decryption D (ks, M) can also be performed easily using the decryption key ks that is provided.
(2) So long as a user does not know the decryption key ks, even if the user knows the encryption key kp and the calculation procedures for the encryption of E (kp, M), and that the encrypted message C=E (kp, M), the user can not ascertain what is contained in the message M because a large number of calculations are required.
When, in addition to the conditions (1) and (2), the following condition (3) is established, the secret communication function can be implemented.
(3) The encryption E (kp, M) can be defined for all the messages (plain text) M, and
D
(
ks, E
(
kp, M
))=
M
is established. That is, anyone can perform the calculations for the encryption E (kp, M) using the public encryption key kp, but only a user who has the secret decryption key ks can perform the calculations for the decryption process D (ks, E (kp, M)) to obtain the contents of message M.
When, in addition to the above conditions (1) and (2), the following condition (4) is established the authenticated communication function can be implemented.
(4) The decryption process D (ks, M) can be defined for all the (plain text) messages M, and
E
(
kp, D
(
ks, M
))=
M
is established. That is, only a user who has the secret decryption key ks can perform the calculations for the decryption process D (ks, M). Even if another user attempts to calculate D (ks′, M) using a bogus secret decryption key ks′, and performs the calculations as would a user who has the secret decryption key ks, the result obtained is
E
(
kp, D
(
ks′, M
)≠
M,
and a recipient would understand that the received information was illegally prepared.
When the value D (ks, M) is altered, the result obtained is
E
(
kp, D
(
ks, M
)′)≠
M,
and a recipient would understand that the received information was illegally prepared.
In the above described encryption method, operation E ( ), for which the public encryption key (hereinafter also referred to as a public key) kp is used, is called “encryption,” and operation D ( ), for which the secret decryption key (hereinafter also referred to as a secret key) ks is used, is called “decryption.”
Therefore, for a secret communication a sender performs the encryption and a recipient performs the decryption, while for an authenticated communication, a sender performs the decryption and a recipient performs the encryption.
The protocols shown below are for a secret communication, an authenticated communication, and a secret communication for a recipient B bearing a signature affixed by a sender A using the public key encryption system.
The secret key of the sender A is ksA and the public key is kpA, and the secret key of the recipient B is ksB and the public key is kpB.
[Secret Communication]
The following procedures are performed for the secret transmission of a (plain text) message M by the sender A to the recipient B.
Step 1: The sender A transmits to the recipient B a message C that is obtained by employing the public key kpB of the recipient B to encrypt the message M as

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