JP5238045B2 - Secure authentication channel - Google Patents

Description

  The present invention relates generally to secure authentication channels, and more particularly to the calculation of session keys for establishing such channels for the protection of digital content, such as in digital television systems.

A secure authentication channel, well known in the field of encryption, is established to allow two mutually authenticated devices (often called peers) to exchange information in a secret manner. The secure authentication channel should preferably have the following characteristics:
Peer mutual authentication key verification ie a common secret is established and at least one peer can prove that the secret is actually common.
Forward secrecy, ie old session keys cannot be calculated even when secret keys (such as authentication secret keys) are known for a long time.

  These properties are formally mathematically provable, and if there is a way around one of the above properties for a given cryptographic protocol, the entire protocol may be broken relatively easily .

  Over the years, the cryptographic community has proposed a number of protocols for secure authentication channels. Only some of these channels have been proven to satisfy the above characteristics.

  All protocols that provide the required characteristics to the channel are several different cryptographic primitives: at least one asymmetric primitive (such as asymmetric encryption or digital signature), hash function, message authentication code (MAC), and some of the above Use other primitives such as symmetric encryption in The problem with these protocols is that they are very resource consuming and difficult to implement in devices that have limited computing power, such as portable security modules such as smart cards. Another problem is that the use of multiple cryptographic primitives makes it difficult to prove that the protocol is secure.

  The present invention provides a secure access channel protocol suitable for implementation in a device having the required characteristics and in particular having limited computational power.

  Throughout this description, it is assumed that the basic concept is well known since encryption is a mature technology. These concepts are not explained beyond what is necessary for understanding the present invention for the sake of simplicity.

  The object of the present invention is to provide a secure access channel protocol suitable for implementation in a device having the required characteristics and in particular having only limited computational power.

In a first aspect, the present invention relates to a method for calculating a session key common to first and second devices (11, 21). The first device has a certificate (C _a ) composed of ^a public key (g ^a ) and an identity (ID _a ) corresponding to the public key (g ^a ), and the corresponding identity (ID _a ) and private key (ID _a ) and a), we know the public key ^{(g a).} The second device has a corresponding certificate and knowledge. The first device selects a first ephemeral private key (x), first ephemeral public key ^{(g x)} is calculated, its certificate and _{(C a)} and the first ephemeral public key ^{(g x)} Transmit to the second device. Upon receiving the first device's certificate (C _a ) and the first ephemeral public key (g ^x ), the second device verifies the first device's certificate (C _a ) and the second ephemeral private key ( y), calculate a second ephemeral public key (g ^y ), calculate an ephemeral shared key (K _eph ) from the first ephemeral public key (g ^x ) and the second ephemeral private key (y), A permanent key (K _perm ) is calculated from the public key (g ^a ) of the first device and its private key (b), a second ephemeral public key (g ^y ), an ephemeral shared key (K _eph ), a permanent key _{(K perm),} a first value from the identity (ID _b) corresponding to itself _{^{(H (g y, K eph}} , K _{erm, ID} b)) is calculated and its certificate _{(C b),} the second ephemeral public key ^{(g y),} the first value ^{_{(H (g y, K eph}} , K perm, ID b) ) To the first device. Receive the second device certificate (C _b ), the second ephemeral public key (g ^y ), and the first value (H (g ^y , K _eph , K _perm , ID _b )) from the second device. Then, the first device verifies the certificate (C _b ) of the second device, and calculates the ephemeral shared key (K _eph ) from the second ephemeral public key (g ^y ) and the first ephemeral private key (x). Then, a permanent key (K _perm ) is calculated from the public key (g ^y ) of the first device and its own private key (a), and the first value (H (g ^y , K _eph , K _perm , ID _b )), The first ephemeral public key (g ^x ), the ephemeral shared key (K _eph ), the permanent key (K _perm ), and the identity (ID _a ) A second value from the ^{_{(H (g x, K eph}} , K perm, ID a)) to the calculated second value ^{_{(H (g x, K eph}} , K perm, ID a)) of the second Send to device. Upon receiving the second value (H (g ^x , K _eph , K _perm , ID _a )), the second device receives the second value (H (g ^x , K _eph , K _perm , ID _a )). verification, and to calculate the session key _{(K sess)} as a function of the ephemeral shared key _{(K eph).} The first device also calculates the session key _{(K sess)} as a function of the ephemeral shared key _{(K eph).}

In a second aspect, the invention relates to a first device (11) that participates in a session key calculation together with a second device (21). The first device has a a certificate from the identity (ID _a) corresponding to themselves and the public key ^{(g a),} the identity (ID _a) corresponding to themselves, the private key (a), We know the public key ^{(g a).} The first device selects an ephemeral private key (x), calculates a first ephemeral public key (g ^x ), and consists of the public key (g ^b ) and the identity of the second device (ID _b ) a certificate _{(C a),} and a first ephemeral public key ^{(g x)} transmitted to the second device, and the certificate of the second device _{(C b),} the second ephemeral public key ^{(g y),} A first value (H (g) calculated from the second ephemeral public key (g ^y ), the ephemeral shared key (K _eph ), the permanent key (K _perm ), and the identity (ID _b ) corresponding to the second device. ^{_{y, K eph, K perm,}} ID b)) receives a from the second device, the certificate of the second device _{(C b)} verifies, the second ephemeral public key g ^y) and the ephemeral calculates a private key (x) from the ephemeral shared key _{(K eph),} the public key of the first device ^{(g b)} and permanent key because his private key and _{(a) (K perm)} Calculate and verify the first value (H (g ^y , K _eph , K _perm , ID _b )), first ephemeral public key (g ^x ), ephemeral shared key (K _eph ), permanent key ( K _perm ) and the identity (ID _a ) corresponding to itself, the second value (H (g ^x , K _eph , K _perm , ID _a )) is calculated, and the second value (H (g ^x , K _eph, flop transmits _K perm, the _ID a)) to the second device calculates the session key _{(K sess)} as a function of the ephemeral shared key _{(K eph)} Processor with a (12).

In a third aspect, the invention relates to a second device (21) that participates in a session key calculation with the first device (11). The second device has a certificate (C _b ) composed of a public key (g ^b ) and an identity corresponding to itself, an identity (ID _b ) corresponding to itself, a private key (b), I know the public key (g ^b ). The second device receives the first device certificate (C _a ) composed of the first device public key (g ^a ) and the identity (ID _a ), and the first ephemeral public key (g ^x ). Then, the ephemeral private key (y) is selected, the second ephemeral public key (g ^y ) is calculated, and the ephemeral shared key (K _eph ) is calculated from the first ephemeral public key (g ^x ) and the ephemeral private key (y). And a permanent key (K _perm ) is calculated from the public key (g ^a ) of the first device and its own private key (b), and the second ephemeral public key (g ^y ) and the ephemeral shared key (K ^y ). and _eph), the permanent key _{(K perm),} from the identity corresponding to itself (ID _b) first Value ^{_{(H (g y, K eph}} , K perm, ID b)) is calculated and its certificate _{(C b),} the second ephemeral public key ^{(g y),} the first value (H ( g ^y , K _eph , K _perm , ID _b )) to the first device. From the first device, the first ephemeral public key (g ^x ), the ephemeral shared key (K _eph ), and the permanent key ( and K _perm), (second value that is calculated from the ^{_{ID a) (H (g x}} , K eph, K perm, ID a) the identity corresponding to the first device receives) the second value ( ^{_{H (g x, K eph,}} K perm, ID a) verifies), a processor (22) for calculating the session key _{(K sess)} as a function of the ephemeral shared key _{(K eph).}

  According to the present invention, it is possible to provide a secure access channel protocol suitable for implementation in a device having required characteristics and particularly having a limited calculation capability.

FIG. 1 illustrates session key exchange according to an embodiment of the present invention.

  FIG. 1 illustrates session key exchange according to an embodiment of the present invention.

Prior to the start of the method, the first device 11 knows its identity ID _a , its own private key a and public key g ^a . g ^a is an abbreviation for g ^a mod p, and as is well known in the art, a is the private key of the first device, g is a known generator, and p is a known prime number. The second device 21 knows the corresponding ID _b , b, g ^b . Certificates of these devices have the public key and identity, ^{_{i.e., C a (g a, ID}} a) and ^{_{C b (g b, ID b}} ) , respectively. Devices 11 and 12 also have processors (CPUs) 12 and 22 that are configured to perform the steps of the method.

In step 252, the first device 11, preferably, the first ephemeral the (ephemeral) private key x is randomly selected, it sends its certificate ^{_{C a (g a, ID a}} ) by the message 254 with The ephemeral public key g ^x is calculated.

Upon receiving the message 254, the second device 21, in step 256, the certificate ^{_{C a (g a, ID a}} ) of the first device 11 verifies. If the verification is unsuccessful, the second device 21 abandons the method. However, if the verification is successful, it is preferably randomly selects a second ephemeral private key y, and a second ephemeral public key ^{g y,} the ephemeral shared key ^{_{K eph = g xy, Diffie-}} Hellman permanent key K _perm = g ^ab is calculated in step 258.

In step 260, the second device 21 determines the second ephemeral public key g ^y , the ephemeral shared key K _eph , Diffie-Hellman permanent key K _perm and its identity ID _b, and one of a number of functions known in the art. The first hash value H (g ^y , K _eph , K _perm , ID _b ) is calculated using an appropriate hash function such as For this reason, an appropriate function other than the hash function may be used for the calculation of the following hash value in this embodiment. The second device 21 then sends the second ephemeral public key g ^y , its certificate C _b (g ^b , ID _b ) and the first hash value H (g ^y , K _eph , K _perm , ID _b ) as a message. It transmits to the 1st apparatus 11 by 262.

Upon receiving the message 262, the first device 11 verifies the certificate C _b (g ^b , ID _b ) of the second device 21 in step 264. If the verification is unsuccessful, the first device 11 abandons the method. However, if the verification is successful, the first device 11 calculates an ephemeral shared key K _eph and a Diffie-Hellman permanent key K _perm in step 266. In step 268, the first device 11 verifies the first hash value using the same hash function as the second device 21 used in step 260. If the first hash value is not authenticated, the first device 11 interrupts the method, but if the first hash value is authenticated, the first device 11 in step 270, the first ephemeral public key g ^x , ephemeral A second hash value H (g ^x , K _eph , K _perm , ID _a ) is calculated using the shared key K _eph , Diffie-Hellman permanent key K _perm and its identity ID _a . The first device 11 transmits the second hash value H (g ^x , K _eph , K _perm , ID _a ) to the second device 21 by the message 272.

Upon receipt of the message 272, the second device 21 utilizes the same hash function as used in step 270 by the first device 10 in step 274 and uses the second hash value H (g ^x , K _eph , K _perm , ID _a ) is verified. If the second hash value is not authenticated, the second device 21 interrupts the protocol, and if the second hash value is authenticated, the second device 21 calculates the hash value of the ephemeral shared key K _eph in step 276. To calculate a session key K _sess . After that, it indicates that the second hash value H (g ^x , K _eph , K _perm , ID _a ) has been successfully authenticated, and the session key K _sess has been calculated. Send to.

Upon receipt of the “ready” message 278 from the second device 21, the first device 11 uses the same hash function as used in step 276 by the second device 21 in step 280 to use the ephemeral shared key K _The same session key K _sess is calculated by calculating the hash value of _eph . The first device 11 then sends a “ready” message 282 to the second device 21 to indicate that it has also calculated the session key K _sess .

At this point, the first device 11 and the second device 21 have a session key K _sess that can be used to protect the information transmitted between them. According to the protocol of the present invention, the confidentiality of the private key is ensured, and authentication and key confirmation are mutually reciprocal. Furthermore, robustness and forward secrecy against previous session key leaks are also guaranteed. Those skilled in the art will appreciate that the three hash functions described with respect to steps 212, 220 and 226 may be different, the same, or two of them may be the same and the other one may be different. Will.

  When this description refers to random numbers, it should be noted that these numbers are often actually pseudo-random.

  The expression “security module” refers to devices such as smart cards, PC cards (formerly known as PCMCIA cards), televisions, etc. that have a processor and can be used to establish a secure authentication channel according to the present invention. It includes any type of security module that is portable or fixed, such as an integrated circuit coupled to a printed circuit board.

  The embodiments described above are particularly suitable for implementation in digital television sets and security modules. However, those skilled in the art will appreciate that the present invention is feasible and can be utilized by any type of device having the necessary resources, ie, a processor, and preferably a memory for storing the necessary information. Will do. Non-limiting specific examples of other devices include a DVD player, a computer that communicates with external accessories, an ATM (Automatic Teller Machine), a bank card, and the like.

11,12 device 12,22 processor

Claims (5)

A first device configured to verify a hash value,
The first device has a certificate composed of a public key and an identity corresponding to the first device, and knows the identity, the private key, and the public key;
The first device is
Select an ephemeral private key,
Calculate the first ephemeral public key,
Sending the certificate and the first ephemeral public key to a second device;
From said second device, said a certificate of the second device comprising the public key and the identity of the second device, the second ephemeral public key and, prior Symbol second ephemeral public key, ephemeral shared key, permanent key And a first hash value calculated from an identity corresponding to the second device,
Verifying the certificate of the second device;
Calculating the ephemeral shared key from the second ephemeral public key and the ephemeral private key;
Calculating the permanent key from the public key of the second device and the private key of the first device;
Verifying the first hash value;
A first device having a processor for. The processor further includes:
Calculating a second hash value by hashing the first ephemeral public key, the ephemeral shared key, the permanent key, and the identity corresponding to the first device;
The first apparatus according to claim 1, wherein the second hash value is transmitted to the second apparatus. A second device configured to verify a hash value,
The second device has a certificate composed of a public key and an identity corresponding to the second device, and knows the identity, the private key, and the public key;
The second device is
Receiving from the first device a certificate of the first device comprised of the public key and identity of the first device and a first ephemeral public key;
Verifying the certificate of the first device;
Select an ephemeral private key,
Calculate the second ephemeral public key,
Calculating an ephemeral shared key from the first ephemeral public key and the ephemeral private key;
A permanent key is calculated from the public key of the first device and the private key of the second device;
Calculating a first hash value by hashing the second ephemeral public key, the ephemeral shared key, the permanent key, and an identity corresponding to the second device;
Sending the second device certificate, the second ephemeral public key, and the first hash value to the first device;
Receiving from the first device a second hash value calculated from the first ephemeral public key, the ephemeral shared key, the permanent key, and an identity corresponding to the first device;
Verifying the second hash value;
A second device having a processor for Verifying a hash value executed by the first device having a certificate composed of a public key and an identity corresponding to the first device and knowing the identity, the private key, and the public key A way to
Selecting an ephemeral private key;
Calculating a first ephemeral public key;
Transmitting the certificate and the first ephemeral public key to a second device;
From the second device, a certificate of the second device comprising the public key and identity of the second device, a second ephemeral public key, the second ephemeral public key, an ephemeral shared key, a permanent key, and Receiving a first hash value calculated by hashing an identity corresponding to the second device;
Verifying the certificate of the second device;
Calculating the ephemeral shared key from the second ephemeral public key and the ephemeral private key;
Calculating the permanent key from a public key of the second device and a private key of the first device;
Verifying the first hash value;
Having a method. Verifying a hash value executed by the second device having a certificate composed of a public key and an identity corresponding to the second device and knowing the identity, the private key, and the public key A way to
Receiving from the first device a certificate of the first device comprised of the public key and identity of the first device and a first ephemeral public key;
Verifying the certificate of the first device;
Selecting an ephemeral private key;
Calculating a second ephemeral public key;
Calculating an ephemeral shared key from the first ephemeral public key and the ephemeral private key;
Calculating a permanent key from the public key of the first device and the private key of the second device;
Calculating a first hash value by hashing the second ephemeral public key, the ephemeral shared key, the permanent key, and an identity corresponding to the second device;
Transmitting the certificate of the second device, the second ephemeral public key, and the first hash value to the first device;
Receiving from the first device a second hash value calculated from the first ephemeral public key, the ephemeral shared key, the permanent key, and an identity corresponding to the first device;
Verifying the second hash value;
Having a method.

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