﻿ Re-keying Mechanisms for Symmetric Keys CryptoPro
18, Suschevsky val Moscow `127018` Russian Federation +7 (495) 995-48-20 svs@cryptopro.ru
General CFRG re-keying, key, key lifetime, encryption mode, mode of operation A certain maximum amount of data can be safely encrypted when encryption is performed under a single key. This amount is called "key lifetime". This specification describes a variety of methods to increase the lifetime of symmetric keys. It provides two types of re-keying mechanisms based on hash functions and on block ciphers, that can be used with modes of operations such as CTR, GCM, CBC, CFB and OMAC.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in .
This document uses the following terms and definitions for the sets and operations on the elements of these sets: the set of all bit strings of a finite length (hereinafter referred to as strings), including the empty string; substrings and string components are enumerated from right to left starting from one; the set of all bit strings of length s, where s is a non-negative integer; the bit length of the bit string X; concatenation of strings A and B both belonging to V*, i.e., a string in V_{|A|+|B|}, where the left substring in V_|A| is equal to A, and the right substring in V_|B| is equal to B; exclusive-or of two bit strings of the same length; ring of residues modulo 2^n; the transformation that maps a string a = (a_s, ... , a_1) in V_s into the integer Int_s(a) = 2^{s-1} * a_s + ... + 2 * a_2 + a_1 (the interpretation of the binary string as an integer); the transformation inverse to the mapping Int_s (the interpretation of an integer as a binary string); the transformation that maps the string a = (a_s, ... , a_1) in V_s into the string MSB_i(a) = (a_s, ... , a_{s-i+1}) in V_i (most significant bits); the transformation that maps the string a = (a_s, ... , a_1) in V_s into the string LSB_i(a) = (a_i, ... , a_1) in V_i (least significant bits); the transformation that maps the string a = (a_s, ... , a_1) in V_s into the string Inc_c(a) = MSB_{|a|-c}(a) | Vec_c(Int_c(LSB_c(a)) + 1(mod 2^c)) in V_s; denotes the string in V_s that consists of s 'a' bits; the block cipher permutation under the key K in V_k; the smallest integer that is greater than or equal to x; the biggest integer that is less than or equal to x; the bit-length of the K; k is assumed to be divisible by 8; the block size of the block cipher (in bits); n is assumed to be divisible by 8; the number of data blocks in the plaintext P (b = ceil(|P|/n)); the section size (the number of bits that are processed with one section key before this key is transformed). A plaintext message P and the corresponding ciphertext C are divided into b = ceil(|P|/n) blocks, denoted P = P_1 | P_2 | ... | P_b and C = C_1 | C_2 | ... | C_b, respectively. The first b-1 blocks P_i and C_i are in V_n, for i = 1, 2, ... , b-1. The b-th blocks P_b, C_b may be an incomplete blocks, i.e., in V_r, where r <= n if not otherwise specified.
Suppose L is an amount of data that can be safely processed with one frame key. For i in {1, 2, ... , t} the frame key K^i (see Figure 4 and Figure 5) should be transformed after processing q_i messages, where q_i can be calculated in accordance with one of the following approaches: Explicit approach: q_i is such that |M^{i,1}| + ... + |M^{i,q_i}| <= L, |M^{i,1}| + ... + |M^{i,q_i+1}| > L. This approach allows to use the frame key K^i in almost optimal way but it can be applied only in case when messages cannot be lost or reordered (e.g., TLS records). Implicit approach: q_i = L / m_max, i = 1, ... , t. The amount of data processed with one frame key K^i is calculated under the assumption that every message has the maximum length m_max. Hence this amount can be considerably less than the key lifetime limitation L. On the other hand, this approach can be applied in case when messages may be lost or reordered (e.g., DTLS records). Dynamic key changes: We can organize the key change using the Protected Point to Point () solution by building a protected tunnel between the endpoints in which the information about frame key updating can be safely passed across. This can be useful, for example, when we wish the adversary not to detect the key change during the protocol evaluation.
External parallel re-keying mechanisms generate frame keys K^1, K^2, ... directly from the initial key K independently of each other. The main idea behind external re-keying with a parallel construction is presented in Figure 4: The frame key K^i, i = 1, ... , t-1, is updated after processing a certain amount of messages (see ).
ExtParallelC re-keying mechanism is based on the key derivation function on a block cipher and is used to generate t frame keys as follows: K^1 | K^2 | ... | K^t = ExtParallelC(K, t * k) = MSB_{t * k}(E_{K}(Vec_n(0)) | E_{K}(Vec_n(1)) | ... | E_{K}(Vec_n(R - 1))), where R = ceil(t * k/n).
ExtParallelH re-keying mechanism is based on the key derivation function HKDF-Expand, described in , and is used to generate t frame keys as follows: K^1 | K^2 | ... | K^t = ExtParallelH(K, t * k) = HKDF-Expand(K, label, t * k), where label is a string (may be a zero-length string) that is defined by a specific protocol.
The application of external tree-based mechanism leads to the construction of the key tree with the initial key K (root key) at the 0-level and the frame keys K^1, K^2, ... at the last level as described in Figure 6. The tree height h and the number of keys Wj, j in {1, ... , h}, which can be partitioned from "parent" key, are defined in accordance with a specific protocol and key lifetime limitations for the used derivation functions. Each j-level key K{j,w}, where j in {1, ... , h}, w in {1, ... , W1 * ... * Wj}, is derived from the (j-1)-level "parent" key K{j-1,ceil(w/Wi)} (and other appropriate input data) using the j-th level derivation function that can be based on the block cipher function or on the hash function and that is defined in accordance with a specific protocol. The i-th frame K^i, i in {1, 2, ... , W1*...*Wh}, can be calculated as follows: K^i = ExtKeyTree(K, i) = KDF_h(KDF_{h-1}(... KDF_1(K, ceil(i / (W2 * ... * Wh)) ... , ceil(i / Wh)), i), where KDF_j is the j-th level derivation function that takes two arguments (the parent key value and the integer in range from 1 to W1 * ... * Wj) and outputs the j-th level key value. The frame key K^i is updated after processing a certain amount of messages (see ). In order to create an efficient implementation, during frame key K^i generation the derivation functions KDF_j, j in {1, ... , h-1}, should be used only in case when ceil(i / (W{j+1} * ... * Wh)) != ceil((i - 1) / (W{j+1} * ... * Wh)); otherwise it is necessary to use previously generated value. This approach also makes it possible to take countermeasures against side channels attacks. Consider an example. Suppose h = 3, W1 = W2 = W3 = W and KDF_1, KDF_2, KDF_3 are key derivation functions based on the KDF_GOSTR3411_2012_256 (hereafter simply KDF) function described in . The resulting ExtKeyTree function can be defined as follows: ExtKeyTree(K, i) = KDF(KDF(KDF(K, "level1", ceil(i / W^2)), "level2", ceil(i / W)), "level3", i). where i in {1, 2, ... , W^3}. The structure similar to external tree-based mechanism can be found in Section 6 of .
External serial re-keying mechanisms generate frame keys, each of which depends on the secret state (K*_1, K*_2, ..., see Figure 5) that is updated after the generation of each new frame key. Similar approaches are used in the protocol, in the updating traffic keys mechanism and were proposed for use in the protocol. External serial re-keying mechanisms have the obvious disadvantage of the impossibility to be implemented in parallel, but they can be preferred if additional forward secrecy is desirable: in case all keys are securely deleted after usage, compromise of a current secret state at some time does not lead to a compromise of all previous secret states and frame keys. In terms of , compromise of application_traffic_secret_N does not compromise all previous application_traffic_secret_i, i < N. The main idea behind external re-keying with a serial construction is presented in Figure 5: The frame key K^i, i = 1, ... , t - 1, is updated after processing a certain amount of messages (see ).
The frame key K^i is calculated using ExtSerialC transformation as follows: K^i = ExtSerialC(K, i) = MSB_k(E_{K*_i}(Vec_n(0)) |E_{K*_i}(Vec_n(1)) | ... | E_{K*_i}(Vec_n(J - 1))), where J = ceil(k / n), i = 1, ... , t, K*_i is calculated as follows: K*_1 = K, K*_{j+1} = MSB_k(E_{K*_j}(Vec_n(J)) | E_{K*_j}(Vec_n(J + 1)) | ... | E_{K*_j}(Vec_n(2 * J - 1))), where j = 1, ... , t - 1.
The frame key K^i is calculated using ExtSerialH transformation as follows: K^i = ExtSerialH(K, i) = HKDF-Expand(K*_i, label1, k), where i = 1, ... , t, HKDF-Expand is the HMAC-based key derivation function, described in , K*_i is calculated as follows: K*_1 = K, K*_{j+1} = HKDF-Expand(K*_j, label2, k), where j = 1, ... , t - 1, where label1 and label2 are different strings from V* that are defined by a specific protocol (see, for example, TLS 1.3 updating traffic keys algorithm ).
In many cases exploiting additional entropy on re-keying won't increase security, but may give a false sense of that, therefore relying on additional entropy must be done with deep studying security in various security models. For example, good PRF constructions do not require additional entropy for the quality of keys so in the most cases there is no need for exploiting additional entropy on external re-keying mechanisms based on secure KDF. However, in some situations mixed-in entropy can still increase security in the case of a time-limited but complete breach of the system, when adversary can access to the frame keys generation interface, but cannot reveal master keys (master keys are stored in an HSM). For example, an external parallel construction based on a KDF on a Hash function with a mixed-in entropy can be described as follows: K^i = HKDF-Expand(K, label_i, k), where label_i is additional entropy that must be sent to the recipient (e.g., be sent jointly with encrypted message). The entropy label_i and the corresponding key K^i must be generated directly before message processing.
Suppose L is an amount of data that can be safely processed with one section key, N is a section size (fixed parameter). Suppose M^{i}_1 is the first section of message M^{i}, i = 1, ... , q (see Figure 9 and Figure 10), then the parameter q can be calculated in accordance with one of the following two approaches: Explicit approach: q_i is such that |M^{1}_1| + ... + |M^{q}_1| <= L, |M^{1}_1| + ... + |M^{q+1}_1| > L This approach allows to use the section key K^i in an almost optimal way but it can be applied only in case when messages cannot be lost or reordered (e.g., TLS records). Implicit approach: q = L / N. The amount of data processed with one section key K^i is calculated under the assumption that the length of every message is equal or greater than section size N and so it can be considerably less than the key lifetime limitation L. On the other hand, this approach can be applied in case when messages may be lost or reordered (e.g., DTLS records).
This section describes the block cipher modes that use the ACPKM re-keying mechanism, which does not use a master key: an initial key is used directly for the data encryption.
This section defines periodical key transformation without a master key, which is called ACPKM re-keying mechanism. This mechanism can be applied to one of the base encryption modes (CTR and GCM block cipher modes) for getting an extension of this encryption mode that uses periodical key transformation without a master key. This extension can be considered as a new encryption mode. An additional parameter that defines functioning of base encryption modes with the ACPKM re-keying mechanism is the section size N. The value of N is measured in bits and is fixed within a specific protocol based on the requirements of the system capacity and the key lifetime. The section size N MUST be divisible by the block size n. The main idea behind internal re-keying without a master key is presented in Figure 9: During the processing of the input message M with the length m in some encryption mode that uses ACPKM key transformation of the initial key K the message is divided into l = ceil(m / N) sections (denoted as M = M_1 | M_2 | ... | M_l, where M_i is in V_N for i in {1, 2, ... , l - 1} and M_l is in V_r, r <= N). The first section of each message is processed with the section key K^1 = K. To process the (i + 1)-th section of each message the section key K^{i+1} is calculated using ACPKM transformation as follows: K^{i+1} = ACPKM(K^i) = MSB_k(E_{K^i}(D_1) | ... | E_{K^i}(D_J)), where J = ceil(k/n) and D_1, D_2, ... , D_J are in V_n and are calculated as follows: D_1 | D_2 | ... | D_J = MSB_{J * n}(D), where D is the following constant in V_{1024}: N o t e : The constant D is such that D_1, ... , D_J are pairwise different for any allowed n and k values. N o t e : The constant D is such that the highest bit of its each octet is equal to 1. This condition is important, as in conjunction with a certain mode message length limitation it allows to prevent collisions of block cipher permutation inputs in cases of key transformation and message processing (for more details see Section 4.4 of ).
This section defines a CTR-ACPKM encryption mode that uses the ACPKM internal re-keying mechanism for the periodical key transformation. The CTR-ACPKM mode can be considered as the base encryption mode CTR (see ) extended by the ACPKM re-keying mechanism. The CTR-ACPKM encryption mode can be used with the following parameters: 64 <= n <= 512; 128 <= k <= 512; the number c of bits in a specific part of the block to be incremented is such that 32 <= c <= 3 / 4 n, c is a multiple of 8; the maximum message size m_max = n * 2^{c-1}. The CTR-ACPKM mode encryption and decryption procedures are defined as follows: The initial counter nonce ICN value for each message that is encrypted under the given initial key K must be chosen in a unique manner.
This section defines GCM-ACPKM authenticated encryption mode that uses the ACPKM internal re-keying mechanism for the periodical key transformation. The GCM-ACPKM mode can be considered as the base authenticated encryption mode GCM (see ) extended by the ACPKM re-keying mechanism. The GCM-ACPKM authenticated encryption mode can be used with the following parameters: n in {128, 256}; 128 <= k <= 512; the number c of bits in a specific part of the block to be incremented is such that 1 / 4 n <= c <= 1 / 2 n, c is a multiple of 8; authentication tag length t; the maximum message size m_max = min{n * (2^{c-1} - 2), 2^{n/2} - 1}. The GCM-ACPKM mode encryption and decryption procedures are defined as follows: The * operation on (pairs of) the 2^n possible blocks corresponds to the multiplication operation for the binary Galois (finite) field of 2^n elements defined by the polynomial f as follows (by analogy with ): f = a^128 + a^7 + a^2 + a^1 + 1, f = a^256 + a^10 + a^5 + a^2 + 1. The initial vector IV value for each message that is encrypted under the given initial key K must be chosen in a unique manner. The key for computing values E_{K}(ICB_0) and H is not updated and is equal to the initial key K.
This section describes the block cipher modes that use the ACPKM-Master re-keying mechanism, which use the initial key K as a master key, so K is never used directly for data processing but is used for key derivation.
This section defines periodical key transformation with a master key, which is called ACPKM-Master re-keying mechanism. This mechanism can be applied to one of the base modes of operation (CTR, GCM, CBC, CFB, OMAC modes) for getting an extension that uses periodical key transformation with a master key. This extension can be considered as a new mode of operation. Additional parameters that define the functioning of modes of operation that use the ACPKM-Master re-keying mechanism are the section size N, the change frequency T* of the master keys K*_1, K*_2, ... (see Figure 10) and the size d of the section key material. The values of N and T* are measured in bits and are fixed within a specific protocol, based on the requirements of the system capacity and the key lifetime. The section size N MUST be divisible by the block size n. The master key frequency T* MUST be divisible by d and by n. The main idea behind internal re-keying with a master key is presented in Figure 10: During the processing of the input message M with the length m in some mode of operation that uses ACPKM-Master key transformation with the initial key K and the master key frequency T* the message M is divided into l = ceil(m / N) sections (denoted as M = M_1 | M_2 | ... | M_l, where M_i is in V_N for i in {1, 2, ... , l - 1} and M_l is in V_r, r <= N). The j-th section of each message is processed with the key material K[j], j in {1, ... , l}, |K[j]| = d, that is calculated with the ACPKM-Master algorithm as follows: K | ... | K[l] = ACPKM-Master(T*, K, d, l) = CTR-ACPKM-Encrypt (T*, K, 1^{n/2}, 0^{d*l}). Note: the parameters d and l MUST be such that d * l <= n * 2^{n/2-1}.
This section defines a CTR-ACPKM-Master encryption mode that uses the ACPKM-Master internal re-keying mechanism for the periodical key transformation. The CTR-ACPKM-Master encryption mode can be considered as the base encryption mode CTR (see ) extended by the ACPKM-Master re-keying mechanism. The CTR-ACPKM-Master encryption mode can be used with the following parameters: 64 <= n <= 512; 128 <= k <= 512; the number c of bits in a specific part of the block to be incremented is such that 32 <= c <= 3 / 4 n, c is a multiple of 8; the maximum message size m_max = min{N * (n * 2^{n/2-1} / k), n * 2^c}. The key material K[j] that is used for one section processing is equal to K^j, |K^j| = k bits. The CTR-ACPKM-Master mode encryption and decryption procedures are defined as follows: The initial counter nonce ICN value for each message that is encrypted under the given initial key must be chosen in a unique manner.
This section defines a GCM-ACPKM-Master authenticated encryption mode that uses the ACPKM-Master internal re-keying mechanism for the periodical key transformation. The GCM-ACPKM-Master authenticated encryption mode can be considered as the base authenticated encryption mode GCM (see ) extended by the ACPKM-Master re-keying mechanism. The GCM-ACPKM-Master authenticated encryption mode can be used with the following parameters: n in {128, 256}; 128 <= k <= 512; the number c of bits in a specific part of the block to be incremented is such that 1 / 4 n <= c <= 1 / 2 n, c is a multiple of 8; authentication tag length t; the maximum message size m_max = min{N * ( n * 2^{n/2-1} / k), n * (2^c - 2), 2^{n/2} - 1}. The key material K[j] that is used for the j-th section processing is equal to K^j, |K^j| = k bits. The GCM-ACPKM-Master mode encryption and decryption procedures are defined as follows: The * operation on (pairs of) the 2^n possible blocks corresponds to the multiplication operation for the binary Galois (finite) field of 2^n elements defined by the polynomial f as follows (by analogy with ): f = a^128 + a^7 + a^2 + a^1 + 1, f = a^256 + a^10 + a^5 + a^2 + 1. The initial vector IV value for each message that is encrypted under the given initial key must be chosen in a unique manner.
This section defines a CBC-ACPKM-Master encryption mode that uses the ACPKM-Master internal re-keying mechanism for the periodical key transformation. The CBC-ACPKM-Master encryption mode can be considered as the base encryption mode CBC (see ) extended by the ACPKM-Master re-keying mechanism. The CBC-ACPKM-Master encryption mode can be used with the following parameters: 64 <= n <= 512; 128 <= k <= 512; the maximum message size m_max = N * (n * 2^{n/2-1} / k). In the specification of the CBC-ACPKM-Master mode the plaintext and ciphertext must be a sequence of one or more complete data blocks. If the data string to be encrypted does not initially satisfy this property, then it MUST be padded to form complete data blocks. The padding methods are out of the scope of this document. An example of a padding method can be found in Appendix A of . The key material K[j] that is used for the j-th section processing is equal to K^j, |K^j| = k bits. We will denote by D_{K} the decryption function which is a permutation inverse to E_{K}. The CBC-ACPKM-Master mode encryption and decryption procedures are defined as follows: The initialization vector IV for each message that is encrypted under the given initial key does not need to be secret, but must be unpredictable.
This section defines a CFB-ACPKM-Master encryption mode that uses the ACPKM-Master internal re-keying mechanism for the periodical key transformation. The CFB-ACPKM-Master encryption mode can be considered as the base encryption mode CFB (see ) extended by the ACPKM-Master re-keying mechanism. The CFB-ACPKM-Master encryption mode can be used with the following parameters: 64 <= n <= 512; 128 <= k <= 512; the maximum message size m_max = N * (n * 2^{n/2-1} / k). The key material K[j] that is used for the j-th section processing is equal to K^j, |K^j| = k bits. The CFB-ACPKM-Master mode encryption and decryption procedures are defined as follows: The initialization vector IV for each message that is encrypted under the given initial key need not to be secret, but must be unpredictable.
This section defines an OMAC-ACPKM-Master message authentication code calculation mode that uses the ACPKM-Master internal re-keying mechanism for the periodical key transformation. The OMAC-ACPKM-Master mode can be considered as the base message authentication code calculation mode OMAC, which is also known as CMAC (see ), extended by the ACPKM-Master re-keying mechanism. The OMAC-ACPKM-Master message authentication code calculation mode can be used with the following parameters: n in {64, 128, 256}; 128 <= k <= 512; the maximum message size m_max = N * (n * 2^{n/2-1} / (k + n)). The key material K[j] that is used for one section processing is equal to K^j | K^j_1, where |K^j| = k and |K^j_1| = n. The following is a specification of the subkey generation process of OMAC: Here R_n takes the following values: n = 64: R_{64} = 0^{59} | 11011; n = 128: R_{128} = 0^{120} | 10000111; n = 256: R_{256} = 0^{145} | 10000100101. The OMAC-ACPKM-Master message authentication code calculation mode is defined as follows:
Both external re-keying and internal re-keying have their own advantages and disadvantages discussed in . For instance, using external re-keying can essentially limit the message length, while in the case of internal re-keying the section size, which can be chosen as the maximal possible for operational properties, limits the amount of separate messages. There is no more preferable technique because the choice of technique can depend on protocol features. However, some protocols may have features that require to take advantages provided by both external and internal re-keying mechanisms: for example, the protocol mainly transmits messages of small length, but it must additionally support very long messages processing. In such situations it is necessary to use external and internal re-keying jointly, since these techniques negate each other's disadvantages. For composition of external and internal re-keying techniques any mechanism described in can be used with any mechanism described in . For example, consider the GCM-ACPKM mode with external serial re-keying based on a KDF on a Hash function. Denote by a frame size the number of messages in each frame (in the case of implicit approach to the key lifetime control) for external re-keying. Let L be a key lifetime limitation. The section size N for internal re-keying and the frame size q for external re-keying must be chosen in such a way that q * N must not exceed L. Suppose that t messages (ICN_i, P_i, A_i), with initial counter nonce ICN_i, plaintext P_i and additional authenticated data A_i, will be processed before renegotiation. For authenticated encryption of each message (ICN_i, P_i, A_i), i = 1, ..., t, the following algorithm can be applied: Note that nonces ICN_i, that are used under the same frame key, must be unique for each message.
Re-keying should be used to increase "a priori" security properties of ciphers in hostile environments (e.g., with side-channel adversaries). If some efficient attacks are known for a cipher, it must not be used. So re-keying cannot be used as a patch for vulnerable ciphers. Base cipher properties must be well analyzed, because the security of re-keying mechanisms is based on the security of a block cipher as a pseudorandom function. Re-keying is not intended to solve any post-quantum security issues for symmetric cryptography, since the reduction of security caused by Grover's algorithm is not connected with a size of plaintext transformed by a cipher - only a negligible (sufficient for key uniqueness) material is needed; and the aim of re-keying is to limit a size of plaintext transformed under one initial key. Re-keying can provide backward security only if previous key material is securely deleted after usage by all parties.
Recommendation for Key Derivation Using Pseudorandom Functions National Institute of Standards and Technology The Transport Layer Security (TLS) Protocol Version 1.2 This document specifies Version 1.2 of the Transport Layer Security (TLS) protocol. The TLS protocol provides communications security over the Internet. The protocol allows client/server applications to communicate in a way that is designed to prevent eavesdropping, tampering, or message forgery. [STANDARDS-TRACK] Datagram Transport Layer Security Version 1.2 This document specifies version 1.2 of the Datagram Transport Layer Security (DTLS) protocol. The DTLS protocol provides communications privacy for datagram protocols. The protocol allows client/server applications to communicate in a way that is designed to prevent eavesdropping, tampering, or message forgery. The DTLS protocol is based on the Transport Layer Security (TLS) protocol and provides equivalent security guarantees. Datagram semantics of the underlying transport are preserved by the DTLS protocol. This document updates DTLS 1.0 to work with TLS version 1.2. [STANDARDS-TRACK] Cryptographic Message Syntax (CMS) This document describes the Cryptographic Message Syntax (CMS). This syntax is used to digitally sign, digest, authenticate, or encrypt arbitrary message content. [STANDARDS-TRACK] The Secure Shell (SSH) Transport Layer Protocol The Secure Shell (SSH) is a protocol for secure remote login and other secure network services over an insecure network. This document describes the SSH transport layer protocol, which typically runs on top of TCP/IP. The protocol can be used as a basis for a number of secure network services. It provides strong encryption, server authentication, and integrity protection. It may also provide compression. Key exchange method, public key algorithm, symmetric encryption algorithm, message authentication algorithm, and hash algorithm are all negotiated. This document also describes the Diffie-Hellman key exchange method and the minimal set of algorithms that are needed to implement the SSH transport layer protocol. [STANDARDS-TRACK] IP Encapsulating Security Payload (ESP) This document describes an updated version of the Encapsulating Security Payload (ESP) protocol, which is designed to provide a mix of security services in IPv4 and IPv6. ESP is used to provide confidentiality, data origin authentication, connectionless integrity, an anti-replay service (a form of partial sequence integrity), and limited traffic flow confidentiality. This document obsoletes RFC 2406 (November 1998). [STANDARDS-TRACK] The Transport Layer Security (TLS) Protocol Version 1.3 Recommendation for Block Cipher Modes of Operation: Galois/Counter Mode (GCM) and GMAC Dworkin, M. Recommendation for Block Cipher Modes of Operation: Methods and Techniques Dworkin, M. Retail Financial Services Symmetric Key Management - Part 3: Derived Unique Key Per Transaction ANSI Increasing the Lifetime of a Key: A Comparative Analysis of the Security of Re-keying Techniques Michel Abdalla and Mihir Bellare On the Practical (In-)Security of 64-bit Block Ciphers: Collision Attacks on HTTP over TLS and OpenVPN Karthikeyan Bhargavan, Gaëtan Leurent TEMPEST attacks against AES. Covertly stealing keys for 200 euro By Craig Ramsay, Jasper Lohuis A Tutorial on Linear and Differential Cryptanalysis Howard M. Heys The Double Ratchet Algorithm Dynamic Key Changes on Encrypted Sessions Peter Alexander On Making U2F Protocol Leakage-Resilient via Re-keying. Key Updating for Leakage Resiliency With Application to AES Modes of Operation A Leakage-Resilient Mode of Operation Practical Leakage-Resilient Symmetric Cryptography How to Construct Random Functions Key Regression: Enabling Efficient Key Distribution for Secure Distributed Storage Secure Group Services for Storage Area Networks One-Way Cross-Trees and Their Applications Towards Sound Fresh Re-Keying with Hard (Physical) Learning Problems Increasing the Lifetime of Symmetric Keys for the GCM Mode by Internal Re-keying
Russ Housley Vigil Security, LLC housley@vigilsec.com Evgeny Alekseev CryptoPro alekseev@cryptopro.ru Ekaterina Smyshlyaeva CryptoPro ess@cryptopro.ru Shay Gueron University of Haifa, Israel Intel Corporation, Israel Development Center, Israel shay.gueron@gmail.com Daniel Fox Franke Akamai Technologies dfoxfranke@gmail.com Lilia Ahmetzyanova CryptoPro lah@cryptopro.ru
We thank Mihir Bellare, Scott Fluhrer, Dorothy Cooley, Yoav Nir, Jim Schaad, Paul Hoffman, Dmitry Belyavsky and Yaron Sheffer for their useful comments.