diff --git a/content/CSE4303/CSE4303_E1.md b/content/CSE4303/CSE4303_E1.md index 3f9d021..d134546 100644 --- a/content/CSE4303/CSE4303_E1.md +++ b/content/CSE4303/CSE4303_E1.md @@ -6,7 +6,7 @@ Time and location – In class exam – Thursday, 3/5 at 11:30 AM – What is allowed: - - One 8.5” X 11” paper of notes, single-sided only, typed or hand-written + - One 8.5" X 11" paper of notes, single-sided only, typed or hand-written Topics covered: @@ -170,7 +170,7 @@ Mallory: Man in the middle, can create and modify packets The message M is called the **plaintext**. Alice will convert plaintext M to an encrypted form using an -encryption algorithm E that outputs a **ciphertext*- C for M. +encryption algorithm E that outputs a **ciphertext** C for M. #### Cryptography goals @@ -234,7 +234,7 @@ In practice, relax this assumption gets "Stream ciphers" Security abstraction: 1. XOR transfers randomness of keystream to randomness of CT regardless of PT’s content -2. Security depends on G being “practically” indistinguishable from random string and “practically” unpredictable +2. Security depends on G being "practically" indistinguishable from random string and "practically" unpredictable 3. Idea: shouldn’t be able to predict next bit of generator given all bits seen so far #### Semantic security @@ -302,15 +302,269 @@ Forward network: - $L_d = R_{d-1},\ \ R_d = L_{d-1} \oplus f_d(R_{d-1})$ - Output: $(L_d, R_d)$ +#### Block ciphers: block modes: ECB + +New attacker model for multi-use keys (e.g. multiple blocks): CPA (Chosen Plaintext)-capable, not just CT-only + +- Attacker sees many PT/CT pairs for same key +- Conservative model: attacker submits arbitrary PT (hence "C"PA) +- Cipher goal: maintain semantic security against CPA + +#### CPA indistinguishability game + +- Updated adversarial game for a CPA attacker: + - Let $E = (E, D)$ be a cipher defined over $(K, M, C)$. For $b \in \{0,1\}$ define $\operatorname{EXP}(b)$ as: + +- Experiment $\operatorname{EXP}(b)$: + - Challenger samples $k \leftarrow K$. + - For each query $i = 1,\ldots,q$: + - Adversary outputs messages $m_{i,0}, m_{i,1} \in M$ such that $|m_{i,0}| = |m_{i,1}|$. + - Challenger returns $c_i \leftarrow E(k, m_{i,b})$. + +- Encryption-oracle access (CPA): + - If the adversary wants $c = E(k, m)$, it queries with $m_{j,0} = m_{j,1} = m$ (so the response is $E(k,m)$ regardless of $b$). + +#### Semantic security under CPA + +- Def: $E$ is semantically secure under CPA if for all "efficient" adversaries $A$, + - $\operatorname{Adv}^{\operatorname{CPA}}[A,E] = \left|\Pr[\operatorname{EXP}(0)=1] - \Pr[\operatorname{EXP}(1)=1]\right|$ + - is negligible. + +### Summary for symmetric encrption + +1. Stream ciphers + - Rely on secure PRG + - No key re-use + - Fast, low-mem, less robust +2. Block ciphers + - Rely on secure PRP + - Allow key re-use (usually only across blocks, not sessions) + - Provide authenticated encryption in some modes (e.g. GCM) + - Slower, higher-mem, more robust + - Used in practice for most crypto tasks (including secure network channels) + ## Hash functions +### Hash function security properties + +- Given a function $h:X \to Y$, we say that $h$ is: + +- 1. Preimage resistant (one-way) if: + - given $y \in Y$ it is computationally infeasible to find a value $x \in X$ s.t. $h(x) = y$ + +- 2. 2nd preimage resistant (weak collision resistant) if: + - given a specific $x \in X$ it is computationally infeasible to find a value $x' \in X$ s.t. $x' \ne x$ and $h(x') = h(x)$ + +- 3. Collision resistant (strong collision resistant) if: + - it is computationally infeasible to find any two distinct values $x', x \in X$ s.t. $h(x') = h(x)$ + +### Collision resistance: adversarial definition + +- Let $H: M \to T$ be a hash function ($|M| \gg |T|$). +- A function $H$ is collision resistant if for all (explicit) "efficient" algorithms $A$, + - $\operatorname{Adv}^{\operatorname{CR}}[A,H] = Pr[$A outputs a collision for $H$ $]$ + - is negligible + +### Hash function integrity applications + +1. Delayed knowledge verification +2. Password storage +3. Trusted timestamping / blockchains +4. Integrity check on software + ## Asymmetric key cryptography +## Asymmetric crypto overview + +- Parties: sender, recipient, attacker (eavesdropping) +- Goal: sender encrypts a plaintext to a ciphertext using a public key; recipient decrypts using a private key. + +#### Public-key encryption system +- Def: a public-key encryption system is a triple of algorithms $(G, E, D)$: + - $G()$: randomized algorithm that outputs a key pair $(pk, sk)$ + - $E(pk, m)$: randomized algorithm that takes $m \in M$ and outputs $c \in C$ + - $D(sk, c)$: deterministic algorithm that takes $c \in C$ and outputs $m \in M$ or $\bot$ +- Consistency: for all $(pk, sk)$ output by $G$, for all $m \in M$, + - $D(sk, E(pk, m)) = m$ + +## Public-key building block: trapdoor function + +#### Trapdoor function +- Def: a trapdoor function $X \to Y$ is a triple of efficient algorithms $(G, F, F^{-1})$: + - $G()$: randomized algorithm that outputs a key pair $(pk, sk)$ + - $F(pk, \cdot)$: deterministic algorithm that defines a function $X \to Y$ + - $F^{-1}(sk, \cdot)$: defines a function $Y \to X$ that inverts $F(pk, \cdot)$ +- More precisely: for all $(pk, sk)$ output by $G$, for all $x \in X$, + - $F^{-1}(sk, F(pk, x)) = x$ + +## Symmetric vs. asymmetric security: attacker models + +- Symmetric ciphers: two security notions for a passive attacker + - One-time security (stream ciphers: ciphertext-only) + - Many-time security (block ciphers: CPA) + - One-time security $\Rightarrow$ many-time security + - Example: ECB mode is one-time secure but not many-time secure +- Public-key encryption: single notion for a passive attacker + - Attacker can encrypt by themselves using the public key + - Therefore one-time security $\Rightarrow$ many-time security (CPA) + - Implication: public-key encryption must be randomized + - Analogous to secure block modes for block ciphers + +## Semantic security of asymmetric crypto (IND-CPA) + +#### IND-CPA game for public-key encryption +- For $b \in \{0,1\}$ define experiments $\mathrm{EXP}(0)$ and $\mathrm{EXP}(1)$: + +- Experiment $\mathrm{EXP}(b)$: + - Challenger runs $(pk, sk) \leftarrow G()$ + - Challenger sends $pk$ to adversary $A$ + - Adversary outputs $m_0, m_1 \in M$ such that $|m_0| = |m_1|$ + - Challenger returns $c \leftarrow E(pk, m_b)$ + - Adversary outputs a bit $b' \in \{0,1\}$ (often modeled as outputting 1 if it "guesses $b=1$") + +#### Semantic security (IND-CPA) +- Def: $E = (G, E, D)$ is semantically secure (a.k.a. IND-CPA) if for all efficient adversaries $A$, + - $\mathrm{Adv}^{\mathrm{SS}}[A, E] = \left|\Pr[\mathrm{EXP}(0)=1] - \Pr[\mathrm{EXP}(1)=1]\right|$ + - is negligible +- Note: inherently multiple-round because the attacker can always encrypt on their own using $pk$ (CPA power is "built in"). + +## RSA cryptosystem: overview + +- Setup: + - $n = pq$, with $p$ and $q$ primes + - Choose $e$ relatively prime to $\phi(n) = (p-1)(q-1)$ + - Choose $d$ as the inverse of $e$ in $\mathbb{Z}_{\phi(n)}$ +- Keys: + - Public key: $K_E = (n, e)$ + - Private key: $K_D = d$ +- Encryption: + - Plaintext $M \in \mathbb{Z}_n$ + - $C = M^e \bmod n$ +- Decryption: + - $M = C^d \bmod n$ + +- Example: + - Setup: + - $p = 7$, $q = 17$ + - $n = 7 \cdot 17 = 119$ + - $\phi(n) = 6 \cdot 16 = 96$ + - $e = 5$ + - $d = 77$ + - Keys: + - public key: $(119, 5)$ + - private key: $77$ + - Encryption: + - $M = 19$ + - $C = 19^5 \bmod 119 = 66$ + - Decryption: + - $M = 66^{77} \bmod 119 = 19$ + +- Security intuition: + - To invert RSA without $d$, attacker must compute $x$ from $c = x^e \pmod n$. + - Best known approach: + - Step 1: factor $n$ (hard) + - Step 2: compute $e$-th roots modulo $p$ and $q$ (easy once factored) + - Notes (as commonly stated in lectures): + - 1024-bit RSA is within reach; 2048-bit is recommended usage + +## Diffie-Hellman key exchange (informal) + +- Fix a large prime $p$ (e.g., 2000 bits) +- Fix an integer $g \in \{1,\ldots,p\}$ + +- Protocol: + - Alice chooses random $a \in \{1,\ldots,p-1\}$ and sends $A = g^a \bmod p$ + - Bob chooses random $b \in \{1,\ldots,p-1\}$ and sends $B = g^b \bmod p$ + - Shared key: + - Alice computes $k_{AB} = B^a \bmod p = g^{ab} \bmod p$ + - Bob computes $k_{AB} = A^b \bmod p = g^{ab} \bmod p$ + +- Hardness assumptions: + - Discrete log problem: given $p, g, y = g^x \bmod p$, find $x$ + - Diffie-Hellman function: $\mathrm{DH}_g(g^a, g^b) = g^{ab} \bmod p$ + +## Diffie-Hellman: security notes + +- As described, the protocol is insecure against active attacks: + - A man-in-the-middle (MiTM) can insert themselves and create 2 separate secure sessions +- Fix idea: need a way to bind identity to a public key + - In practice: web of trust (e.g., GPG) or Public Key Infrastructure (PKI) + +## Implementing trapdoor functions securely + +- Never encrypt by applying $F$ directly to plaintext: + - Deterministic: cannot be semantically secure + - Many attacks exist for concrete TDFs + - Same plaintext blocks yield same ciphertext blocks + +- Naive (insecure) sketch: + - $E(pk, m)$: output $c \leftarrow F(pk, m)$ + - $D(sk, c)$: output $F^{-1}(sk, c)$ + +## Public-key encryption from TDFs + +- Components: + - $(G, F, F^{-1})$: secure TDF $X \to Y$ + - $(E_s, D_s)$: symmetric authenticated encryption over $(K, M, C)$ + - $H: X \to K$: a hash function + +- Construction of $(G, E, D)$ (with $G$ same as in the TDF): + - $E(pk, m)$: + - sample $x \leftarrow X$, compute $y \leftarrow F(pk, x)$ + - derive $k \leftarrow H(x)$, compute $c \leftarrow E_s(k, m)$ + - output $(y, c)$ + - $D(sk, (y, c))$: + - compute $x \leftarrow F^{-1}(sk, y)$ + - derive $k \leftarrow H(x)$, compute $m \leftarrow D_s(k, c)$ + - output $m$ + +- Visual intuition: + - header: $y = F(pk, x)$ + - body: $c = E_s(H(x), m)$ + +- Security theorem (lecture-style statement): + - If $(G, F, F^{-1})$ is a secure TDF, $(E_s, D_s)$ provides authenticated encryption, and $H$ is modeled as a random oracle, then $(G, E, D)$ is CCA-secure in the random oracle model (often denoted CCA-RO). + - Extension exists to reach full CCA (outside the RO idealization). + +## Wrapup: symmetric vs. asymmetric systems + +- Symmetric: faster, but key distribution is hard +- Asymmetric: slower, but key distribution/management is easier +- Application: secure web sessions (e.g., online shopping) + - Use symmetric-key encrypted sessions for bulk traffic + - Exchange symmetric keys using an asymmetric scheme + - Authenticate public keys (PKI or web of trust) + +## Key exchange: summary + +- Symmetric-key encryption challenges: + - Key storage: one per user pair, $O(n^2)$ total for $n$ users + - Key exchange: how to do it over a non-secure channel? + +- Possible solutions: + +- 1) Trusted Third Party (TTP) + - All users establish separate secret keys with the TTP + - TTP helps manage user-user keys (storage and secure channel) + - Applicability: + - Works for local domains + - Popular implementation: Kerberos for Single Sign On (SSO) + - Challenges: + - Scale: central authentication server is not suitable for the entire Internet + - Latency: requires online response from central server for every user-user session + +- 2) Public/private keys with certificates + - All users have a single stable public key (helps with key storage and exchange) + - Users exchange per-session symmetric keys via a secure channel using public/private keys + - Trusting public keys: binding is validated by a third-party authority (Certificate Authority, CA) + - Why better than TTP? CAs can validate statically by issuing certificates, then be uninvolved + - CA/certificate process covered in a future lecture + ## Appendix for additional algorithms and methods ### Feistel network (used by several items below) -A **Feistel network*- splits a block into left/right halves and iterates rounds of the form $(L_{i+1},R_{i+1})=(R_i, L_i\oplus F(R_i,K_i))$, so decryption reuses the same structure with subkeys in reverse order. +A **Feistel network** splits a block into left/right halves and iterates rounds of the form $(L_{i+1},R_{i+1})=(R_i, L_i\oplus F(R_i,K_i))$, so decryption reuses the same structure with subkeys in reverse order. Feistel-based here: **DES, 3DES, CAMELLIA, SEED, GOST 28147-89 (and thus GOST89MAC uses a Feistel block cipher internally).** @@ -318,21 +572,21 @@ Feistel-based here: **DES, 3DES, CAMELLIA, SEED, GOST 28147-89 (and thus GOST89M These don’t implement encryption or authentication; they just include/exclude suites. -- **COMPLEMENTOFDEFAULT*- — (selection) picks suites in `ALL` that are not enabled by default (notably RC4/anonymous, depending on build). -- **ALL*- — (selection) all suites except `eNULL`, in a default preference order (OpenSSL-defined ordering). -- **COMPLEMENTOFALL*- — (selection) suites excluded from `ALL` (currently `eNULL`). -- **HIGH / MEDIUM / LOW*- — (selection) groups suites by effective key strength class (OpenSSL policy buckets). -- **TLSv1.2 / TLSv1.0 / SSLv3*- — (selection) restricts to suites whose *minimum supported protocol version- is at least that value. -- **SUITEB128 / SUITEB128ONLY / SUITEB192*- — (selection) enforces “Suite B”-style constraints: only very specific ECDHE-ECDSA-AES-GCM suites and curves/hashes. -- **CBC*- — (mode selector) selects suites using **CBC mode*- for symmetric encryption (confidentiality only unless paired with a MAC). +- **COMPLEMENTOFDEFAULT** — (selection) picks suites in `ALL` that are not enabled by default (notably RC4/anonymous, depending on build). +- **ALL** — (selection) all suites except `eNULL`, in a default preference order (OpenSSL-defined ordering). +- **COMPLEMENTOFALL** — (selection) suites excluded from `ALL` (currently `eNULL`). +- **HIGH / MEDIUM / LOW** — (selection) groups suites by effective key strength class (OpenSSL policy buckets). +- **TLSv1.2 / TLSv1.0 / SSLv3** — (selection) restricts to suites whose *minimum supported protocol version- is at least that value. +- **SUITEB128 / SUITEB128ONLY / SUITEB192** — (selection) enforces "Suite B"-style constraints: only very specific ECDHE-ECDSA-AES-GCM suites and curves/hashes. +- **CBC** — (mode selector) selects suites using **CBC mode** for symmetric encryption (confidentiality only unless paired with a MAC). --- -### B) “No encryption” / “no authentication” flags +### B) "No encryption" / "no authentication" flags -- **eNULL, NULL*- — **encryption/decryption: none**; **cipher method: N/A**; core idea: the record payload is not encrypted at all (plaintext). -- **aNULL*- — **authentication: none*- (no peer authentication); **cipher method: N/A**; core idea: uses anonymous key agreement (no cert/signature), enabling MITM. -- **ADH / AECDH*- — **authentication: none**; **cipher method: N/A**; core idea: anonymous (EC)DH establishes a shared secret but without identity binding → MITM-friendly. +- **eNULL, NULL** — **encryption/decryption: none**; **cipher method: N/A**; core idea: the record payload is not encrypted at all (plaintext). +- **aNULL** — **authentication: none** (no peer authentication); **cipher method: N/A**; core idea: uses anonymous key agreement (no cert/signature), enabling MITM. +- **ADH / AECDH** — **authentication: none**; **cipher method: N/A**; core idea: anonymous (EC)DH establishes a shared secret but without identity binding → MITM-friendly. --- @@ -342,63 +596,63 @@ These describe *how keys are negotiated- and/or *how the peer is authenticated*, #### RSA / DH / ECDH families -- **kRSA, RSA*- — (key exchange) the premaster secret is sent encrypted under the server’s RSA public key (classic TLS RSA KX). -- **aRSA, aECDSA, aDSS, aGOST, aGOST01*- — (authentication) the server identity is proven via a certificate signature scheme (RSA / ECDSA / DSA / GOST). -- **kDHr, kDHd, kDH*- — (key exchange) *static- DH key agreement using DH certificates (obsolete/removed in newer OpenSSL). -- **kDHE, kEDH, DH / DHE, EDH / ECDHE, EECDH / kEECDH, kECDHE, ECDH*- — (key exchange) *ephemeral- (EC)DH derives a fresh shared secret each handshake; “authenticated” variants bind it to a cert/signature. -- **aDH*- — (authentication selector) indicates DH-authenticated suites (DH certs; also removed in newer OpenSSL). +- **kRSA, RSA** — (key exchange) the premaster secret is sent encrypted under the server’s RSA public key (classic TLS RSA KX). +- **aRSA, aECDSA, aDSS, aGOST, aGOST01** — (authentication) the server identity is proven via a certificate signature scheme (RSA / ECDSA / DSA / GOST). +- **kDHr, kDHd, kDH** — (key exchange) *static- DH key agreement using DH certificates (obsolete/removed in newer OpenSSL). +- **kDHE, kEDH, DH / DHE, EDH / ECDHE, EECDH / kEECDH, kECDHE, ECDH** — (key exchange) *ephemeral- (EC)DH derives a fresh shared secret each handshake; "authenticated" variants bind it to a cert/signature. +- **aDH** — (authentication selector) indicates DH-authenticated suites (DH certs; also removed in newer OpenSSL). #### PSK family -- **PSK*- — (keying model) uses a pre-shared secret as the authentication/secret basis. -- **kPSK, kECDHEPSK, kDHEPSK, kRSAPSK*- — (key exchange) PSK combined with (EC)DHE or RSA to derive/transport session keys. -- **aPSK*- — (authentication) PSK itself authenticates endpoints (except RSA_PSK where cert auth may be involved). +- **PSK** — (keying model) uses a pre-shared secret as the authentication/secret basis. +- **kPSK, kECDHEPSK, kDHEPSK, kRSAPSK** — (key exchange) PSK combined with (EC)DHE or RSA to derive/transport session keys. +- **aPSK** — (authentication) PSK itself authenticates endpoints (except RSA_PSK where cert auth may be involved). --- -### D) Symmetric encryption / AEAD (this is where “block vs stream” applies) +### D) Symmetric encryption / AEAD (this is where "block vs stream" applies) #### AES family -- **AES128 / AES256 / AES*- — **encryption/decryption**; **block cipher**; core algorithm: AES is an SPN (substitution–permutation network) of repeated SubBytes/ShiftRows/MixColumns/AddRoundKey rounds. -- **AESGCM*- — **both encryption + message authentication (AEAD)**; **both*- (AES block cipher used in counter mode + auth); core algorithm: encrypt with AES-CTR and authenticate with GHASH over ciphertext/AAD to produce a tag. -- **AESCCM / AESCCM8*- — **both encryption + message authentication (AEAD)**; **both**; core algorithm: compute CBC-MAC then encrypt with CTR mode, with 16-byte vs 8-byte tag length variants. +- **AES128 / AES256 / AES** — **encryption/decryption**; **block cipher**; core algorithm: AES is an SPN (substitution–permutation network) of repeated SubBytes/ShiftRows/MixColumns/AddRoundKey rounds. +- **AESGCM** — **both encryption + message authentication (AEAD)**; **both** (AES block cipher used in counter mode + auth); core algorithm: encrypt with AES-CTR and authenticate with GHASH over ciphertext/AAD to produce a tag. +- **AESCCM / AESCCM8** — **both encryption + message authentication (AEAD)**; **both**; core algorithm: compute CBC-MAC then encrypt with CTR mode, with 16-byte vs 8-byte tag length variants. #### ARIA family -- **ARIA128 / ARIA256 / ARIA*- — **encryption/decryption**; **block cipher**; core algorithm: ARIA is an SPN-style block cipher with byte-wise substitutions and diffusion layers across rounds. +- **ARIA128 / ARIA256 / ARIA** — **encryption/decryption**; **block cipher**; core algorithm: ARIA is an SPN-style block cipher with byte-wise substitutions and diffusion layers across rounds. #### CAMELLIA family -- **CAMELLIA128 / CAMELLIA256 / CAMELLIA*- — **encryption/decryption**; **block cipher**; core algorithm: Camellia is a **Feistel network*- with round functions plus extra FL/FL$^{-1}$ layers for nonlinearity and diffusion. *(Feistel: yes)* +- **CAMELLIA128 / CAMELLIA256 / CAMELLIA** — **encryption/decryption**; **block cipher**; core algorithm: Camellia is a **Feistel network** with round functions plus extra FL/FL$^{-1}$ layers for nonlinearity and diffusion. *(Feistel: yes)* #### ChaCha20 -- **CHACHA20*- — **encryption/decryption**; **stream cipher**; core algorithm: ChaCha20 generates a keystream via repeated ARX (add-rotate-xor) quarter-rounds on a 512-bit state and XORs it with plaintext. +- **CHACHA20** — **encryption/decryption**; **stream cipher**; core algorithm: ChaCha20 generates a keystream via repeated ARX (add-rotate-xor) quarter-rounds on a 512-bit state and XORs it with plaintext. #### DES / 3DES -- **DES*- — **encryption/decryption**; **block cipher**; core algorithm: DES is a 16-round **Feistel network*- using expansion, S-boxes, and permutations. *(Feistel: yes)* -- **3DES*- — **encryption/decryption**; **block cipher**; core algorithm: applies DES three times (EDE or EEE) to increase effective security while retaining the **Feistel*- DES core. *(Feistel: yes)* +- **DES** — **encryption/decryption**; **block cipher**; core algorithm: DES is a 16-round **Feistel network** using expansion, S-boxes, and permutations. *(Feistel: yes)* +- **3DES** — **encryption/decryption**; **block cipher**; core algorithm: applies DES three times (EDE or EEE) to increase effective security while retaining the **Feistel** DES core. *(Feistel: yes)* #### RC4 -- **RC4*- — **encryption/decryption**; **stream cipher**; core algorithm: maintains a 256-byte permutation and produces a keystream byte-by-byte that is XORed with plaintext. +- **RC4** — **encryption/decryption**; **stream cipher**; core algorithm: maintains a 256-byte permutation and produces a keystream byte-by-byte that is XORed with plaintext. #### RC2 / IDEA / SEED -- **RC2*- — **encryption/decryption**; **block cipher**; core algorithm: mixes key-dependent operations (adds, XORs, rotates) across rounds with “mix” and “mash” steps (not Feistel). -- **IDEA*- — **encryption/decryption**; **block cipher**; core algorithm: combines modular addition, modular multiplication, and XOR in a Lai–Massey-like structure to achieve diffusion/nonlinearity (not Feistel). -- **SEED*- — **encryption/decryption**; **block cipher**; core algorithm: a 16-round **Feistel network*- with nonlinear S-box-based round functions. *(Feistel: yes)* +- **RC2** — **encryption/decryption**; **block cipher**; core algorithm: mixes key-dependent operations (adds, XORs, rotates) across rounds with "mix" and "mash" steps (not Feistel). +- **IDEA** — **encryption/decryption**; **block cipher**; core algorithm: combines modular addition, modular multiplication, and XOR in a Lai–Massey-like structure to achieve diffusion/nonlinearity (not Feistel). +- **SEED** — **encryption/decryption**; **block cipher**; core algorithm: a 16-round **Feistel network** with nonlinear S-box-based round functions. *(Feistel: yes)* --- ### E) Hash / MAC / digest selectors (message authentication side) -These are not “ciphers” but are used for integrity/authentication (often as HMAC, PRF, signatures). +These are not "ciphers" but are used for integrity/authentication (often as HMAC, PRF, signatures). -- **MD5*- — **message authentication component*- (typically via HMAC, historically); **cipher method: N/A**; core algorithm: iterated Merkle–Damgård hash compressing 512-bit blocks into a 128-bit digest (now considered broken for collision resistance). -- **SHA1, SHA*- — **message authentication component*- (typically HMAC-SHA1 historically); **N/A**; core algorithm: Merkle–Damgård hash producing 160-bit output via 80-step compression (collisions known). -- **SHA256 / SHA384*- — **message authentication component*- (HMAC / TLS PRF / signatures); **N/A**; core algorithm: SHA-2 family Merkle–Damgård hashes with different word sizes/output lengths (256-bit vs 384-bit). -- **GOST94*- — **message authentication component*- (HMAC based on GOST R 34.11-94); **N/A**; core algorithm: builds an HMAC tag by hashing inner/outer padded key with the message using the GOST hash. -- **GOST89MAC*- — **message authentication**; **block-cipher-based MAC (so “block” internally)**; core algorithm: computes a MAC using the GOST 28147-89 block cipher in a MAC mode (cipher-based chaining). *(Feistel internally via GOST 28147-89)* +- **MD5** — **message authentication component** (typically via HMAC, historically); **cipher method: N/A**; core algorithm: iterated Merkle–Damgård hash compressing 512-bit blocks into a 128-bit digest (now considered broken for collision resistance). +- **SHA1, SHA** — **message authentication component** (typically HMAC-SHA1 historically); **N/A**; core algorithm: Merkle–Damgård hash producing 160-bit output via 80-step compression (collisions known). +- **SHA256 / SHA384** — **message authentication component** (HMAC / TLS PRF / signatures); **N/A**; core algorithm: SHA-2 family Merkle–Damgård hashes with different word sizes/output lengths (256-bit vs 384-bit). +- **GOST94** — **message authentication component** (HMAC based on GOST R 34.11-94); **N/A**; core algorithm: builds an HMAC tag by hashing inner/outer padded key with the message using the GOST hash. +- **GOST89MAC** — **message authentication**; **block-cipher-based MAC (so "block" internally)**; core algorithm: computes a MAC using the GOST 28147-89 block cipher in a MAC mode (cipher-based chaining). *(Feistel internally via GOST 28147-89)*