diff --git a/Cargo.lock b/Cargo.lock
index e63687beb..5cabd2c1e 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1,5 +1,7 @@
 # This file is automatically @generated by Cargo.
 # It is not intended for manual editing.
+version = 3
+
 [[package]]
 name = "aes"
 version = "0.6.0"
@@ -93,6 +95,12 @@ version = "1.0.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "cdb031dd78e28731d87d56cc8ffef4a8f36ca26c38fe2de700543e627f8a464a"
 
+[[package]]
+name = "base64ct"
+version = "1.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8a32fd6af2b5827bce66c29053ba0e7c42b9dcab01835835058558c10851a46b"
+
 [[package]]
 name = "bech32"
 version = "0.8.1"
@@ -138,6 +146,20 @@ dependencies = [
  "serde",
 ]
 
+[[package]]
+name = "bip0039"
+version = "0.8.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ac4d1925000f9183da41ed95477ea815512b5bb7e06e6c6964986ca077e2b75c"
+dependencies = [
+ "hmac",
+ "pbkdf2",
+ "rand",
+ "sha2",
+ "unicode-normalization",
+ "zeroize",
+]
+
 [[package]]
 name = "bitflags"
 version = "1.2.1"
@@ -294,7 +316,7 @@ checksum = "69323bff1fb41c635347b8ead484a5ca6c3f11914d784170b158d8449ab07f8e"
 dependencies = [
  "cfg-if 0.1.10",
  "crossbeam-channel 0.4.4",
- "crossbeam-deque",
+ "crossbeam-deque 0.7.3",
  "crossbeam-epoch 0.8.2",
  "crossbeam-queue",
  "crossbeam-utils 0.7.2",
@@ -331,6 +353,17 @@ dependencies = [
  "maybe-uninit",
 ]
 
+[[package]]
+name = "crossbeam-deque"
+version = "0.8.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6455c0ca19f0d2fbf751b908d5c55c1f5cbc65e03c4225427254b46890bdde1e"
+dependencies = [
+ "cfg-if 1.0.0",
+ "crossbeam-epoch 0.9.5",
+ "crossbeam-utils 0.8.5",
+]
+
 [[package]]
 name = "crossbeam-epoch"
 version = "0.8.2"
@@ -397,6 +430,16 @@ version = "0.1.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "a2f4a431c5c9f662e1200b7c7f02c34e91361150e382089a8f2dec3ba680cbda"
 
+[[package]]
+name = "crypto-mac"
+version = "0.11.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b1d1a86f49236c215f271d40892d5fc950490551400b02ef360692c29815c714"
+dependencies = [
+ "generic-array",
+ "subtle",
+]
+
 [[package]]
 name = "crypto_api"
 version = "0.2.2"
@@ -488,6 +531,12 @@ dependencies = [
  "zeroize",
 ]
 
+[[package]]
+name = "either"
+version = "1.6.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e78d4f1cc4ae33bbfc157ed5d5a5ef3bc29227303d595861deb238fcec4e9457"
+
 [[package]]
 name = "endian-type"
 version = "0.1.2"
@@ -497,7 +546,7 @@ checksum = "c34f04666d835ff5d62e058c3995147c06f42fe86ff053337632bca83e42702d"
 [[package]]
 name = "equihash"
 version = "0.1.0"
-source = "git+https://github.com/zcash/librustzcash.git?rev=1a40fc9ac82bf43da15cb36d3757fdf610be1bd2#1a40fc9ac82bf43da15cb36d3757fdf610be1bd2"
+source = "git+https://github.com/zcash/librustzcash.git?rev=98dc330cdb1c96e980e62b5bc901edbaa128fea2#98dc330cdb1c96e980e62b5bc901edbaa128fea2"
 dependencies = [
  "blake2b_simd",
  "byteorder",
@@ -636,15 +685,14 @@ dependencies = [
 [[package]]
 name = "halo2"
 version = "0.0.1"
-source = "git+https://github.com/zcash/halo2.git?rev=d04b532368d05b505e622f8cac4c0693574fbd93#d04b532368d05b505e622f8cac4c0693574fbd93"
+source = "git+https://github.com/zcash/halo2.git?rev=27c4187673a9c6ade13fbdbd4f20955530c22d7f#27c4187673a9c6ade13fbdbd4f20955530c22d7f"
 dependencies = [
  "blake2b_simd",
- "crossbeam-utils 0.8.5",
  "ff",
  "group",
- "num_cpus",
  "pasta_curves",
  "rand",
+ "rayon",
 ]
 
 [[package]]
@@ -671,6 +719,16 @@ version = "0.4.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "7f24254aa9a54b5c858eaee2f5bccdb46aaf0e486a595ed5fd8f86ba55232a70"
 
+[[package]]
+name = "hmac"
+version = "0.11.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2a2a2320eb7ec0ebe8da8f744d7812d9fc4cb4d09344ac01898dbcb6a20ae69b"
+dependencies = [
+ "crypto-mac",
+ "digest",
+]
+
 [[package]]
 name = "http"
 version = "0.2.4"
@@ -770,8 +828,7 @@ checksum = "dd25036021b0de88a0aff6b850051563c6516d0bf53f8638938edbb9de732736"
 [[package]]
 name = "jubjub"
 version = "0.7.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "593fc4726ca80edb47ee18ab4d826719e25c2096991a79308b44fb915c6014ef"
+source = "git+https://github.com/zkcrypto/jubjub.git?rev=96ab4162b83303378eae32a326b54d88b75bffc2#96ab4162b83303378eae32a326b54d88b75bffc2"
 dependencies = [
  "bitvec",
  "bls12_381",
@@ -1060,10 +1117,11 @@ checksum = "624a8340c38c1b80fd549087862da4ba43e08858af025b236e509b6649fc13d5"
 [[package]]
 name = "orchard"
 version = "0.0.0"
-source = "git+https://github.com/zcash/orchard.git?rev=74df35ce890726478983fb892ff38a5e44ceb08a#74df35ce890726478983fb892ff38a5e44ceb08a"
+source = "git+https://github.com/zcash/orchard.git?rev=8454f86d423edbf0b53a1d5d32df1c691f8b7188#8454f86d423edbf0b53a1d5d32df1c691f8b7188"
 dependencies = [
  "aes",
  "arrayvec 0.7.1",
+ "bigint",
  "bitvec",
  "blake2b_simd",
  "ff",
@@ -1124,6 +1182,17 @@ dependencies = [
  "winapi",
 ]
 
+[[package]]
+name = "password-hash"
+version = "0.2.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "fd482dfb8cfba5a93ec0f91e1c0f66967cb2fdc1a8dba646c4f9202c5d05d785"
+dependencies = [
+ "base64ct",
+ "rand_core 0.6.3",
+ "subtle",
+]
+
 [[package]]
 name = "pasta_curves"
 version = "0.1.1"
@@ -1139,6 +1208,16 @@ dependencies = [
  "subtle",
 ]
 
+[[package]]
+name = "pbkdf2"
+version = "0.8.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d95f5254224e617595d2cc3cc73ff0a5eaf2637519e25f03388154e9378b6ffa"
+dependencies = [
+ "crypto-mac",
+ "password-hash",
+]
+
 [[package]]
 name = "pin-project"
 version = "1.0.8"
@@ -1290,6 +1369,31 @@ dependencies = [
  "bitflags",
 ]
 
+[[package]]
+name = "rayon"
+version = "1.5.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c06aca804d41dbc8ba42dfd964f0d01334eceb64314b9ecf7c5fad5188a06d90"
+dependencies = [
+ "autocfg",
+ "crossbeam-deque 0.8.1",
+ "either",
+ "rayon-core",
+]
+
+[[package]]
+name = "rayon-core"
+version = "1.9.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d78120e2c850279833f1dd3582f730c4ab53ed95aeaaaa862a2a5c71b1656d8e"
+dependencies = [
+ "crossbeam-channel 0.5.1",
+ "crossbeam-deque 0.8.1",
+ "crossbeam-utils 0.8.5",
+ "lazy_static",
+ "num_cpus",
+]
+
 [[package]]
 name = "reddsa"
 version = "0.0.0"
@@ -1503,6 +1607,21 @@ dependencies = [
  "winapi",
 ]
 
+[[package]]
+name = "tinyvec"
+version = "1.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "848a1e1181b9f6753b5e96a092749e29b11d19ede67dfbbd6c7dc7e0f49b5338"
+dependencies = [
+ "tinyvec_macros",
+]
+
+[[package]]
+name = "tinyvec_macros"
+version = "0.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cda74da7e1a664f795bb1f8a87ec406fb89a02522cf6e50620d016add6dbbf5c"
+
 [[package]]
 name = "tokio"
 version = "1.9.0"
@@ -1606,6 +1725,15 @@ version = "1.13.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "879f6906492a7cd215bfa4cf595b600146ccfac0c79bcbd1f3000162af5e8b06"
 
+[[package]]
+name = "unicode-normalization"
+version = "0.1.19"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d54590932941a9e9266f0832deed84ebe1bf2e4c9e4a3554d393d18f5e854bf9"
+dependencies = [
+ "tinyvec",
+]
+
 [[package]]
 name = "unicode-xid"
 version = "0.2.2"
@@ -1674,7 +1802,7 @@ dependencies = [
 [[package]]
 name = "zcash_address"
 version = "0.0.0"
-source = "git+https://github.com/zcash/librustzcash.git?rev=1a40fc9ac82bf43da15cb36d3757fdf610be1bd2#1a40fc9ac82bf43da15cb36d3757fdf610be1bd2"
+source = "git+https://github.com/zcash/librustzcash.git?rev=98dc330cdb1c96e980e62b5bc901edbaa128fea2#98dc330cdb1c96e980e62b5bc901edbaa128fea2"
 dependencies = [
  "bech32",
  "blake2b_simd",
@@ -1684,7 +1812,7 @@ dependencies = [
 [[package]]
 name = "zcash_history"
 version = "0.2.0"
-source = "git+https://github.com/zcash/librustzcash.git?rev=1a40fc9ac82bf43da15cb36d3757fdf610be1bd2#1a40fc9ac82bf43da15cb36d3757fdf610be1bd2"
+source = "git+https://github.com/zcash/librustzcash.git?rev=98dc330cdb1c96e980e62b5bc901edbaa128fea2#98dc330cdb1c96e980e62b5bc901edbaa128fea2"
 dependencies = [
  "bigint",
  "blake2b_simd",
@@ -1694,7 +1822,7 @@ dependencies = [
 [[package]]
 name = "zcash_note_encryption"
 version = "0.0.0"
-source = "git+https://github.com/zcash/librustzcash.git?rev=1a40fc9ac82bf43da15cb36d3757fdf610be1bd2#1a40fc9ac82bf43da15cb36d3757fdf610be1bd2"
+source = "git+https://github.com/zcash/librustzcash.git?rev=98dc330cdb1c96e980e62b5bc901edbaa128fea2#98dc330cdb1c96e980e62b5bc901edbaa128fea2"
 dependencies = [
  "blake2b_simd",
  "byteorder",
@@ -1708,9 +1836,10 @@ dependencies = [
 [[package]]
 name = "zcash_primitives"
 version = "0.5.0"
-source = "git+https://github.com/zcash/librustzcash.git?rev=1a40fc9ac82bf43da15cb36d3757fdf610be1bd2#1a40fc9ac82bf43da15cb36d3757fdf610be1bd2"
+source = "git+https://github.com/zcash/librustzcash.git?rev=98dc330cdb1c96e980e62b5bc901edbaa128fea2#98dc330cdb1c96e980e62b5bc901edbaa128fea2"
 dependencies = [
  "aes",
+ "bip0039",
  "bitvec",
  "blake2b_simd",
  "blake2s_simd",
@@ -1738,7 +1867,7 @@ dependencies = [
 [[package]]
 name = "zcash_proofs"
 version = "0.5.0"
-source = "git+https://github.com/zcash/librustzcash.git?rev=1a40fc9ac82bf43da15cb36d3757fdf610be1bd2#1a40fc9ac82bf43da15cb36d3757fdf610be1bd2"
+source = "git+https://github.com/zcash/librustzcash.git?rev=98dc330cdb1c96e980e62b5bc901edbaa128fea2#98dc330cdb1c96e980e62b5bc901edbaa128fea2"
 dependencies = [
  "bellman",
  "blake2b_simd",
diff --git a/Cargo.toml b/Cargo.toml
index b31dcdf5b..80f8f7ebc 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -64,11 +64,12 @@ codegen-units = 1
 
 [patch.crates-io]
 ed25519-zebra = { git = "https://github.com/ZcashFoundation/ed25519-zebra.git", rev = "d3512400227a362d08367088ffaa9bd4142a69c7" }
-halo2 = { git = "https://github.com/zcash/halo2.git", rev = "d04b532368d05b505e622f8cac4c0693574fbd93" }
+halo2 = { git = "https://github.com/zcash/halo2.git", rev = "27c4187673a9c6ade13fbdbd4f20955530c22d7f" }
 incrementalmerkletree = { git = "https://github.com/zcash/incrementalmerkletree", rev = "8b59049f1746827ffa3763efa8af948f680491d0" }
-orchard = { git = "https://github.com/zcash/orchard.git", rev = "74df35ce890726478983fb892ff38a5e44ceb08a" }
-zcash_address = { git = "https://github.com/zcash/librustzcash.git", rev = "1a40fc9ac82bf43da15cb36d3757fdf610be1bd2" }
-zcash_history = { git = "https://github.com/zcash/librustzcash.git", rev = "1a40fc9ac82bf43da15cb36d3757fdf610be1bd2" }
-zcash_note_encryption = { git = "https://github.com/zcash/librustzcash.git", rev = "1a40fc9ac82bf43da15cb36d3757fdf610be1bd2" }
-zcash_primitives = { git = "https://github.com/zcash/librustzcash.git", rev = "1a40fc9ac82bf43da15cb36d3757fdf610be1bd2" }
-zcash_proofs = { git = "https://github.com/zcash/librustzcash.git", rev = "1a40fc9ac82bf43da15cb36d3757fdf610be1bd2" }
+jubjub = { git = "https://github.com/zkcrypto/jubjub.git", rev = "96ab4162b83303378eae32a326b54d88b75bffc2" }
+orchard = { git = "https://github.com/zcash/orchard.git", rev = "8454f86d423edbf0b53a1d5d32df1c691f8b7188" }
+zcash_address = { git = "https://github.com/zcash/librustzcash.git", rev = "98dc330cdb1c96e980e62b5bc901edbaa128fea2" }
+zcash_history = { git = "https://github.com/zcash/librustzcash.git", rev = "98dc330cdb1c96e980e62b5bc901edbaa128fea2" }
+zcash_note_encryption = { git = "https://github.com/zcash/librustzcash.git", rev = "98dc330cdb1c96e980e62b5bc901edbaa128fea2" }
+zcash_primitives = { git = "https://github.com/zcash/librustzcash.git", rev = "98dc330cdb1c96e980e62b5bc901edbaa128fea2" }
+zcash_proofs = { git = "https://github.com/zcash/librustzcash.git", rev = "98dc330cdb1c96e980e62b5bc901edbaa128fea2" }
diff --git a/src/rust/include/rust/zip339.h b/src/rust/include/rust/zip339.h
new file mode 100644
index 000000000..fa5b0d378
--- /dev/null
+++ b/src/rust/include/rust/zip339.h
@@ -0,0 +1,59 @@
+#ifndef ZCASH_RUST_INCLUDE_RUST_ZIP339_H
+#define ZCASH_RUST_INCLUDE_RUST_ZIP339_H
+
+#include "rust/types.h"
+
+#include <stddef.h>
+#include <stdint.h>
+
+#ifndef __cplusplus
+  #include <assert.h>
+#endif
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+    // These must match src/rust/src/zip339_ffi.rs.
+    // (They happen to also match the integer values correspond in the bip0039-rs crate with the
+    // "all-languages" feature enabled, but that's not required.)
+    enum Language
+#ifdef __cplusplus
+    : uint32_t
+#endif
+    {
+        English = 0,
+        SimplifiedChinese = 1,
+        TraditionalChinese = 2,
+        Czech = 3,
+        French = 4,
+        Italian = 5,
+        Japanese = 6,
+        Korean = 7,
+        Portuguese = 8,
+        Spanish = 9,
+        SIZE_HACK = 0xFFFFFFFF // needed when compiling as C
+    };
+
+    static_assert(sizeof(Language) == 4);
+
+    /// Creates a phrase with the given entropy, in the given `Language`. The phrase is represented as
+    /// a pointer to a null-terminated C string that must not be written to, and must be freed by
+    /// `zip339_free_phrase`.
+    const char * zip339_entropy_to_phrase(Language language, const uint8_t *entropy, size_t entropy_len);
+
+    /// Frees a phrase returned by `zip339_entropy_to_phrase`.
+    void zip339_free_phrase(const char *phrase);
+
+    /// Returns `true` if the given string is a valid mnemonic phrase in the given `Language`.
+    bool zip339_validate_phrase(Language language, const char *phrase);
+
+    /// Copies the seed for the given phrase into the 64-byte buffer `buf`.
+    /// Returns true if successful, false on error. In case of error, `buf` is zeroed.
+    bool zip339_phrase_to_seed(Language language, const char *phrase, uint8_t (*buf)[64]);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif // ZCASH_RUST_INCLUDE_RUST_ZIP339_H
diff --git a/src/rust/src/rustzcash.rs b/src/rust/src/rustzcash.rs
index 09ba1bd87..cc5e1f232 100644
--- a/src/rust/src/rustzcash.rs
+++ b/src/rust/src/rustzcash.rs
@@ -72,6 +72,7 @@ mod address_ffi;
 mod history_ffi;
 mod orchard_ffi;
 mod transaction_ffi;
+mod zip339_ffi;
 
 mod test_harness_ffi;
 
diff --git a/src/rust/src/tests/mod.rs b/src/rust/src/tests/mod.rs
index 2d1e35041..cea15547b 100644
--- a/src/rust/src/tests/mod.rs
+++ b/src/rust/src/tests/mod.rs
@@ -10,6 +10,7 @@ mod key_components;
 mod mmr;
 mod notes;
 mod signatures;
+mod zip339;
 
 #[test]
 fn sapling_generators() {
diff --git a/src/rust/src/tests/zip339.rs b/src/rust/src/tests/zip339.rs
new file mode 100644
index 000000000..8ee72ec00
--- /dev/null
+++ b/src/rust/src/tests/zip339.rs
@@ -0,0 +1,120 @@
+use libc::c_char;
+use std::{
+    convert::{TryFrom, TryInto},
+    ffi::CStr,
+    ptr,
+};
+
+use crate::zip339_ffi::{
+    zip339_entropy_to_phrase, zip339_free_phrase, zip339_phrase_to_seed, zip339_validate_phrase,
+    Language,
+};
+use zcash_primitives::zip339;
+
+#[test]
+fn test_try_from_language() {
+    assert_eq!(Language(0).try_into(), Ok(zip339::Language::English));
+    assert!(zip339::Language::try_from(Language(1234)).is_err());
+}
+
+#[test]
+#[should_panic]
+fn test_null_entropy_to_phrase_panics() {
+    zip339_entropy_to_phrase(Language(0), ptr::null(), 0);
+}
+
+#[test]
+fn test_free_null_phrase_is_noop() {
+    zip339_free_phrase(ptr::null_mut());
+}
+
+#[test]
+#[should_panic]
+fn test_validate_null_phrase_panics() {
+    zip339_validate_phrase(Language(0), ptr::null());
+}
+
+#[test]
+#[should_panic]
+fn test_null_phrase_to_seed_panics() {
+    zip339_phrase_to_seed(Language(0), ptr::null(), ptr::NonNull::dangling().as_ptr());
+}
+
+#[test]
+#[should_panic]
+fn test_phrase_to_seed_with_null_buffer_panics() {
+    zip339_phrase_to_seed(
+        Language(0),
+        ptr::NonNull::dangling().as_ptr(),
+        ptr::null_mut(),
+    );
+}
+
+#[test]
+fn test_known_answers() {
+    let mut entropy = [0u8; 32];
+
+    // English and another language with non-Latin script.
+    let expected_phrase_en = "abandon abandon abandon abandon abandon abandon abandon abandon \
+        abandon abandon abandon abandon abandon abandon abandon abandon \
+        abandon abandon abandon abandon abandon abandon abandon art";
+    let expected_phrase_ko = "가격 가격 가격 가격 가격 가격 가격 가격 \
+        가격 가격 가격 가격 가격 가격 가격 가격 \
+        가격 가격 가격 가격 가격 가격 가격 계단";
+
+    let expected_seed_en = [
+        0x40, 0x8B, 0x28, 0x5C, 0x12, 0x38, 0x36, 0x00, 0x4F, 0x4B, 0x88, 0x42, 0xC8, 0x93, 0x24,
+        0xC1, 0xF0, 0x13, 0x82, 0x45, 0x0C, 0x0D, 0x43, 0x9A, 0xF3, 0x45, 0xBA, 0x7F, 0xC4, 0x9A,
+        0xCF, 0x70, 0x54, 0x89, 0xC6, 0xFC, 0x77, 0xDB, 0xD4, 0xE3, 0xDC, 0x1D, 0xD8, 0xCC, 0x6B,
+        0xC9, 0xF0, 0x43, 0xDB, 0x8A, 0xDA, 0x1E, 0x24, 0x3C, 0x4A, 0x0E, 0xAF, 0xB2, 0x90, 0xD3,
+        0x99, 0x48, 0x08, 0x40,
+    ];
+    let expected_seed_ko = [
+        0xD6, 0x93, 0x5F, 0x34, 0x3A, 0xC6, 0x66, 0x97, 0x58, 0x06, 0xDF, 0xA7, 0xBD, 0x0E, 0x45,
+        0xF8, 0x3A, 0x6F, 0x0A, 0x1A, 0x9F, 0x48, 0x54, 0xF4, 0x40, 0xEC, 0x09, 0x0B, 0xE3, 0xEF,
+        0x16, 0xEA, 0x09, 0x42, 0x03, 0xEC, 0x07, 0xA1, 0x7D, 0x8B, 0x43, 0x9B, 0xBD, 0x2F, 0x89,
+        0x3D, 0xB8, 0xB8, 0x3D, 0x3E, 0x43, 0xD4, 0x59, 0xA3, 0x6C, 0x29, 0xDF, 0xAB, 0xC2, 0xF9,
+        0xF5, 0xB2, 0x47, 0x72,
+    ];
+
+    for &(expected_phrase, expected_seed, language) in [
+        (expected_phrase_en, expected_seed_en, Language(0)),
+        (expected_phrase_ko, expected_seed_ko, Language(7)),
+    ]
+    .iter()
+    {
+        // Testing these all together simplifies memory management in the test code.
+
+        // test zip339_entropy_to_phrase
+        let phrase = zip339_entropy_to_phrase(language, entropy[..].as_mut_ptr(), 32);
+        assert_eq!(
+            unsafe { CStr::from_ptr(phrase) }.to_str().unwrap(),
+            expected_phrase
+        );
+
+        // test zip339_validate_phrase
+        assert!(zip339_validate_phrase(language, phrase));
+        assert!(!zip339_validate_phrase(Language(1), phrase));
+        assert!(!zip339_validate_phrase(Language(1234), phrase));
+
+        // test zip339_phrase_to_seed
+        let mut seed = [0u8; 64];
+        assert!(zip339_phrase_to_seed(
+            language,
+            phrase,
+            seed[..].as_mut_ptr()
+        ));
+        assert_eq!(seed, expected_seed);
+
+        // test that zip339_phrase_to_seed zeros buffer on failure
+        let mut seed = [0xFFu8; 64];
+        assert!(!zip339_phrase_to_seed(
+            Language(1),
+            phrase,
+            seed[..].as_mut_ptr()
+        ));
+        assert_eq!(seed, [0u8; 64]);
+
+        zip339_free_phrase(phrase as *mut c_char);
+    }
+}
diff --git a/src/rust/src/zip339_ffi.rs b/src/rust/src/zip339_ffi.rs
new file mode 100644
index 000000000..eeafa5bcd
--- /dev/null
+++ b/src/rust/src/zip339_ffi.rs
@@ -0,0 +1,111 @@
+use libc::{c_char, size_t};
+use std::{
+    convert::{TryFrom, TryInto},
+    ffi::{CStr, CString},
+    ptr, slice,
+};
+
+use zcash_primitives::zip339;
+
+// It's safer to use a wrapper type here than an enum. We can't stop a C caller from passing
+// an unrecognized value as a `language` parameter; if it were an enum on the Rust side,
+// then that would immediately be UB, whereas this way we can return null or false.
+#[repr(C)]
+#[derive(Copy, Clone)]
+pub struct Language(pub u32);
+
+impl TryFrom<Language> for zip339::Language {
+    type Error = ();
+
+    fn try_from(language: Language) -> Result<Self, ()> {
+        // These must match `src/rust/include/zip339.h`.
+        match language {
+            Language(0) => Ok(zip339::Language::English),
+            Language(1) => Ok(zip339::Language::SimplifiedChinese),
+            Language(2) => Ok(zip339::Language::TraditionalChinese),
+            Language(3) => Ok(zip339::Language::Czech),
+            Language(4) => Ok(zip339::Language::French),
+            Language(5) => Ok(zip339::Language::Italian),
+            Language(6) => Ok(zip339::Language::Japanese),
+            Language(7) => Ok(zip339::Language::Korean),
+            Language(8) => Ok(zip339::Language::Portuguese),
+            Language(9) => Ok(zip339::Language::Spanish),
+            Language(_) => Err(()),
+        }
+    }
+}
+
+/// Creates a phrase with the given entropy, in the given `Language`. The phrase is represented as
+/// a pointer to a null-terminated C string that must not be written to, and must be freed by
+/// `zip339_free_phrase`.
+#[no_mangle]
+pub extern "C" fn zip339_entropy_to_phrase(
+    language: Language,
+    entropy: *const u8,
+    entropy_len: size_t,
+) -> *const c_char {
+    assert!(!entropy.is_null());
+
+    if let Ok(language) = language.try_into() {
+        let entropy = unsafe { slice::from_raw_parts(entropy, entropy_len) }.to_vec();
+        if let Ok(mnemonic) = zip339::Mnemonic::from_entropy_in(language, entropy) {
+            if let Ok(phrase) = CString::new(mnemonic.phrase()) {
+                return phrase.into_raw() as *const c_char;
+            }
+        }
+    }
+    ptr::null()
+}
+
+/// Frees a phrase returned by `zip339_entropy_to_phrase`.
+#[no_mangle]
+pub extern "C" fn zip339_free_phrase(phrase: *const c_char) {
+    if !phrase.is_null() {
+        unsafe {
+            // It is correct to cast away const here; the memory is not actually immutable.
+            CString::from_raw(phrase as *mut c_char);
+        }
+    }
+}
+
+/// Returns `true` if the given string is a valid mnemonic phrase in the given `Language`.
+#[no_mangle]
+pub extern "C" fn zip339_validate_phrase(language: Language, phrase: *const c_char) -> bool {
+    assert!(!phrase.is_null());
+
+    if let Ok(language) = language.try_into() {
+        if let Ok(phrase) = unsafe { CStr::from_ptr(phrase) }.to_str() {
+            return zip339::Mnemonic::validate_in(language, phrase).is_ok();
+        }
+    }
+    false
+}
+
+/// Copies the seed for the given phrase into the 64-byte buffer `buf`.
+/// Returns true if successful, false on error. In case of error, `buf` is zeroed.
+#[no_mangle]
+pub extern "C" fn zip339_phrase_to_seed(
+    language: Language,
+    phrase: *const c_char,
+    buf: *mut u8,
+) -> bool {
+    assert!(!phrase.is_null());
+    assert!(!buf.is_null());
+
+    if let Ok(language) = language.try_into() {
+        if let Ok(phrase) = unsafe { CStr::from_ptr(phrase) }.to_str() {
+            if let Ok(mnemonic) = zip339::Mnemonic::from_phrase_in(language, phrase) {
+                // Use the empty passphrase.
+                let seed = mnemonic.to_seed("");
+                unsafe {
+                    ptr::copy(seed.as_ptr(), buf, 64);
+                }
+                return true;
+            }
+        }
+    }
+    unsafe {
+        ptr::write_bytes(buf, 0, 64);
+    }
+    false
+}
diff --git a/src/test/data/unified_addrs.json b/src/test/data/unified_addrs.json
index 51ee6f806..dd14807df 100644
--- a/src/test/data/unified_addrs.json
+++ b/src/test/data/unified_addrs.json
@@ -1,14 +1,15 @@
 [
     ["From https://github.com/zcash-hackworks/zcash-test-vectors/blob/master/unified_address.py"],
     ["p2pkh_bytes, p2sh_bytes, sapling_raw_addr, orchard_raw_addr, unified_addr"],
-    [null, "7a8f739a2d9e945b0ce152a8049e294c4d6e66b1", null, "dcb1d2a37762148db4cee3bbf19fb1ec05891894b13801c622ba6a90faf1119f8224ae3985c6abd3b7bbae", "753178356b66326a646c37396b7170653964757a7a3979667a796a726437327364613671657032393265367a336c6c61767270796a6d7674363436306e6733667163773672636479656e6468756a6834643263767979357432687878347364787973326d76346767637a64327a676e73616166707835706173673532646d3237306574757a3778797877657539"],
-    ["b3534201cfb1cd8dbf69b8250c18ef41294ca979", null, "902b6565a1c44e7e7a080571af1dd774697cc126f1fc0435d3cdbf868783e9fb4620df4bf175cbf2c3e36f", "05f61273a7201295332fee4579474534809a0aeb817a2bc0594166ad7a462067712533b6eec0fa2d1be99f", "7531383863733339306532376632346877676468396573756532796b73386c3230743271367864686a39646d32396c3877376d34726438336473706d72743271336435746e36376e367379736e7438306872387a676e6377376b38386735306e6376367874653835676b676e707a79647037747367677166343533723464787164356d6b78757561377938343871747a65383365763777366a676d6a7738363935793475337a7778326671637a6b6875687938356a6764746a72343339366a6d6467643937383768663739783634786b32646e6a70"],
-    [null, "e8c7203d996af7d477083756d59af80d06a745f4", null, "4ea7d6b3dfa338192af06cbbf47ad405715bc7832bedb1466217dc0d93314de9f3c25eec89f9a21bfe0e93", "753179763478336d786e3364787a3033746b76336575646861683878637838366d6633717667326a397a6c61656a676b716c366633797a6d6e7479387576363868366774616a38677a676c71676d7775723061646b686765307671636e74617668393335307437387a79637772346c363463746633716e3934637472797338356e6c3476306c77383270767173"],
-    [null, null, "02f1536b622c01346742d8f90e9d4ff39137f1bebe6e23ad9971776b3372702494cc08951eef032b35350f", null, "753135716632787236373076337971796b6374397663716c7935687079766b6d68386b3371636c7135367664686d7030386336717a30726c6e763467307168613975736e6c37336b713539376838763363377274717765303575326836637035706374767a7a346c7463"],
-    [null, "183e31d49f25c9a138f49b1a537edcf04be34a98", "3246b59a5b492dab1855cc176bddfa28418f11f97f7b361cc3e8834b2c30d2a1717df323ef98ea7de71d2e", "ab6d26252c521547049de208283d96278bb221a6874cb5a86af1d3f8b3db3fbee3dbefedcb2c71e3ca1ead", "753130657a616879367071307034687a65703666376564706775376c67777530796372366c6c6463796a36713530356e67617672706b766534357461396861776571666c3361763768323977346d633777636a7a3871686a797132726e6d6861387271716b34616d3861713461346a6d743263326e6a37746368653765647571367968613536766b73343971706c77786b707761333666676864367036336c796763706339796774773964617630786366326d787270387530367474683468676732383937307368796468637871796a79726b3235"],
-    [null, null, "970dc3450d34554141d356cb548056279c57708fa73bd16ffe9a2e24ea694898a7b8af1b0ff92585d02623", "0414bb62b86149ee731851f27d532ac0361169da46e6d53d19d3dfd07a5bae22969922d8d0af7dc1e13bae", "753163723077393538346b6133676d6a70687a63636b306736367676786e38723266647566636a707477367534346165327379756b6b6d7a7763716673776b65776e7a6d7a7a7571736c73793733637178706d68336d797967756e6b6e6d73676d746c7a716b7436686e7461687973676a767a77307133707a647865757666747978647a6870726873666a6b3374686e686d706730706834666d36386b7035386d653336386464657066647671356e77726c"],
-    [null, "098b79535e790fe53e29fef2b3766697ac32b4f4", "a8a8797c1ba69f78672affa65b943975026931ea628431f0991e744872ac9f36946f5dcd6851a0b5af29cf", "678ab0079bea28bf165c1ab976a2a58c18a7811ca2ad0ad649e876273d04325da6ca53cdb83c111e8e4394", "7531676e333576786d3030666b713430636c647a76717372767037336e36726b383036306e6b39686d6c77376535323070346a73757265756b6e757738726c6a7166336e71766130347434326b6e66753071716e39666c6830676e707a766d673868653070747272326e6c38306a787a666178723039656739323035727273727265737a7339306c63633876737561636836773535777334337738637577716d3768736e387234343361617370366d6533327177346c7639666533393978333370783861767865636b656d763976327867366b6e37"],
-    [null, null, "3509c9e069e89fe501d97622c283ac98923da2d7e6eb346b4bafa67865e1e6dae7cf213b1ea3648dc09b48", null, "753165686465736a6a647370336839376a787a6361766b686433327032706173306a6b333274783577736d707a6a6c35783534306835353335636c6677686b6b686c3367716370726d7779653279793239306a66706378716a71756c616a766a76357571786e7463656e"],
-    [null, "30d069896cff30eb414f727b89e001afa2fb8dc3", "55bc46aea6f60c1d61915640029b2af6334d7d27e1c47a248ab47c9fbe5d2d7bb5818739f062e37136654c", null, "7531766e63346a336e6a6b377174706a65767764743877347a356e30376b3670363277396a673977796d6a6c7530776d766d7570357579656a61613736646b646778797337653661646e7865636678636e6c39306571366539723035647379353274363976653961756e6b376a773270337477726175686e6c3638346d6e77336332757968616a366c70346c33"],
-    [null, null, "5c26a8117729334a957ca7941d47b2ce7040e844fa9882c25bfd2fcf51fa8ab21376f5300d0123f5703e9e", null, "75317279687461366d73356a617375396e76653232396d7639383664677a39366a6c37357232716c6d78797061363775657276373834727235306663677567766b646767327773726e7877737378756c77306c7a387735373970746a3239777567383867673577337a73"]
+    [null, "7a8f739a2d9e945b0ce152a8049e294c4d6e66b1", null, "dcb1d2a37762148db4cee3bbf19fb1ec05891894b13801c622ba6a90faf1119f8224ae3985c6abd3b7bbae", "75316532386638787a6e656d676574797872647a6b66676a756773667839646b713274686e657a65396c333474707674706d656a656774643567686b7768676a7268736466646e74336b34736632757939656138637461756d7a7075646c657a356667756c77716b70753566766a77796374747a79646c383664373434613430617175747a687a7674797a6e68"],
+    ["b3534201cfb1cd8dbf69b8250c18ef41294ca979", null, "902b6565a1c44e7e7a080571af1dd774697cc126f1fc0435d3cdbf868783e9fb4620df4bf175cbf2c3e36f", "05f61273a7201295332fee4579474534809a0aeb817a2bc0594166ad7a462067712533b6eec0fa2d1be99f", "75313371733278796b66737464343332777076366368367336636b683473346833736372746435686b6179367277366a6e3667656e3734726d76636136357775736771653637716d6b6b667a79686c6b7767383071796a33726363616e68356667377a73393032793234676e3271796636706b636363686730356a7a70337972666e3470753861746538673771397239737465767832383434357235776e3378333570663771713332346e746878747a6377786576796661346c326d326d327873376564766570396674613476747776686b617878"],
+    [null, "e8c7203d996af7d477083756d59af80d06a745f4", null, "4ea7d6b3dfa338192af06cbbf47ad405715bc7832bedb1466217dc0d93314de9f3c25eec89f9a21bfe0e93", "75317270776b64357837746534657a636d6c716172676b66336372737066716b686d787766737170713032346a6173733267373465347233367a70353071737333766863743732736163687573306b37303578796768756c726a786364777764617130716a6e6e737366326676616b7a7a386634367077387263613933366665796566366d6c36657137776c6c"],
+    [null, null, "02f1536b622c01346742d8f90e9d4ff39137f1bebe6e23ad9971776b3372702494cc08951eef032b35350f", null, "7531396468786d38386776637739747774767a6b7537637a376a753372767075356a766832637138676d38716465766e6c34657365793833667a7239796d666133676a6d6d6b3472786a3279703838677478646b71676e6a366e6e717974667568303875796335667572"],
+    [null, "183e31d49f25c9a138f49b1a537edcf04be34a98", "3246b59a5b492dab1855cc176bddfa28418f11f97f7b361cc3e8834b2c30d2a1717df323ef98ea7de71d2e", "ab6d26252c521547049de208283d96278bb221a6874cb5a86af1d3f8b3db3fbee3dbefedcb2c71e3ca1ead", "75313563327972666a7774743636336e713068707173683678746a793238387a7476616375616c37336d666675723338336d7465706339687278743374703465613568373830706733686b35756a326775393770326c756d39716a6836327872613763336879366e6471327877686737657138713736766632386333326437766d6c337a323934767438656374636c773672307032336e64703578647a666578633971773065777572796e6a353235736b78376d306a756b636a7265616b6a3261703332376b6a7172767567656435667930737a79"],
+    [null, null, "970dc3450d34554141d356cb548056279c57708fa73bd16ffe9a2e24ea694898a7b8af1b0ff92585d02623", "0414bb62b86149ee731851f27d532ac0361169da46e6d53d19d3dfd07a5bae22969922d8d0af7dc1e13bae", "75317a6467397a376c7732713037357977396e306a376668387279756a73726a727237347a71783939337463736874666d6d3271786b74763372303438653774723471356a38736665703367396e76387770786639767472336a7a6e6d6d35367a3775706a6530356b7a766d75726d706371703034633033377a32646833356364383232357874336b34376e7a6668327974737630376d337438676433337035723276376b66656739343571376a63306768"],
+    [null, "098b79535e790fe53e29fef2b3766697ac32b4f4", "a8a8797c1ba69f78672affa65b943975026931ea628431f0991e744872ac9f36946f5dcd6851a0b5af29cf", "678ab0079bea28bf165c1ab976a2a58c18a7811ca2ad0ad649e876273d04325da6ca53cdb83c111e8e4394", "7531796a7733366d7a777a346a643879746e726436676b68376179676d656a3272746c716733766a397965656866646b3233356a657336727170666a6c777167333776346d653575676a6c7a72646e68676c383872726c6567383378386130716d77797a7936393872387675636e346877616772367163657a7373663663683074373466633068766e366d373737687037353761766632636b7a63333239357033323430716c7675707964656c37336c377163746e343063796b357536736573617772367a6d6b746c6a6678687163633765773468"],
+    [null, null, "3509c9e069e89fe501d97622c283ac98923da2d7e6eb346b4bafa67865e1e6dae7cf213b1ea3648dc09b48", null, "753171786b796d6b68647a6372727a6c79346672717563646b66736e6a377776776c716575306b3466337472706e657a3476777a75686b64616a6b356537363437346d6a34396b75653978396866776566386d34377363633861703933686e6773657567333864706371"],
+    [null, "30d069896cff30eb414f727b89e001afa2fb8dc3", "55bc46aea6f60c1d61915640029b2af6334d7d27e1c47a248ab47c9fbe5d2d7bb5818739f062e37136654c", null, "75316433726b71777a396b37346b7475766c746e32746d746a36676b6c6739336877733937797473337a75363038766b76673363327973686d6d3330713668386b6434727433733076703475616a776668396137356538613837306e39346c6b70657835617337716e77333436346e7261747563356e35793575766e7a7666326d3466656a687a6576686e306d"],
+    [null, null, "5c26a8117729334a957ca7941d47b2ce7040e844fa9882c25bfd2fcf51fa8ab21376f5300d0123f5703e9e", null, "75316166617430647574617379666b736161766d34726c336178716e75786c777437363573393476397a716a7430397a793633646c356d6d7970397835636b7672756c6d647134636b6a337272763766396c37756e78666c306438723635383234746773677276673071"]
 ]
+