diff --git a/Cargo.lock b/Cargo.lock
index fd43b6f0..cd21ade6 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -323,6 +323,12 @@ dependencies = [
  "windows-link",
 ]
 
+[[package]]
+name = "cmov"
+version = "0.5.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0c9ea0ac24bc397ab3c98583a3c9ba74fa56b09a4449bbe172b9b1ddb016027a"
+
 [[package]]
 name = "const-oid"
 version = "0.9.6"
@@ -335,6 +341,12 @@ version = "0.8.7"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "773648b94d0e5d620f64f280777445740e61fe701025087ec8b57f45c791888b"
 
+[[package]]
+name = "cpubits"
+version = "0.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "15b85f9c39137c3a891689859392b1bd49812121d0d61c9caf00d46ed5ce06ae"
+
 [[package]]
 name = "cpufeatures"
 version = "0.2.17"
@@ -378,6 +390,17 @@ dependencies = [
  "zeroize",
 ]
 
+[[package]]
+name = "crypto-bigint"
+version = "0.7.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1a52aa3fcda4e6302a9f48734f234d35d4721b96f8fe07d073f07ce9df4f0271"
+dependencies = [
+ "cpubits",
+ "ctutils",
+ "num-traits",
+]
+
 [[package]]
 name = "crypto-common"
 version = "0.1.6"
@@ -404,6 +427,15 @@ version = "0.0.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "e2931af7e13dc045d8e9d26afccc6fa115d64e115c9c84b1166288b46f6782c2"
 
+[[package]]
+name = "ctutils"
+version = "0.4.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7d5515a3834141de9eafb9717ad39eea8247b5674e6066c404e8c4b365d2a29e"
+dependencies = [
+ "cmov",
+]
+
 [[package]]
 name = "curve25519-dalek"
 version = "4.1.3"
@@ -638,7 +670,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b5e6043086bf7973472e0c7dff2142ea0b680d30e18d9cc40f267efbf222bd47"
 dependencies = [
  "base16ct",
- "crypto-bigint",
+ "crypto-bigint 0.5.5",
  "digest",
  "ff",
  "generic-array",
@@ -1343,7 +1375,7 @@ name = "refund-policy-vdf"
 version = "0.1.0"
 dependencies = [
  "accensa-common",
- "crypto-bigint",
+ "crypto-bigint 0.7.5",
  "soroban-sdk",
 ]
 
diff --git a/contracts/refund-policy-vdf/Cargo.toml b/contracts/refund-policy-vdf/Cargo.toml
index 125175b1..124b07c8 100644
--- a/contracts/refund-policy-vdf/Cargo.toml
+++ b/contracts/refund-policy-vdf/Cargo.toml
@@ -19,7 +19,7 @@ accensa-common = { workspace = true }
 # Wesolowski VDF verification (issue #138): big-integer modular exponentiation
 # in pure WASM. `default-features = false` keeps it no_std / no rand; it adds
 # no new crates over what the vault previously pulled in transitively.
-crypto-bigint = { version = "0.5.5", default-features = false }
+crypto-bigint = { version = "0.7.5", default-features = false }
 
 [dev-dependencies]
 soroban-sdk = { workspace = true, features = ["testutils"] }
\ No newline at end of file