diff --git a/matrix_sdk/src/sas.rs b/matrix_sdk/src/sas.rs
index 2f995ef9..3cff3faa 100644
--- a/matrix_sdk/src/sas.rs
+++ b/matrix_sdk/src/sas.rs
@@ -63,7 +63,7 @@ impl Sas {
     }
 
     /// Get the decimal version of the short auth string.
-    pub fn decimals(&self) -> Option<(u32, u32, u32)> {
+    pub fn decimals(&self) -> Option<(u16, u16, u16)> {
         self.inner.decimals()
     }
 
diff --git a/matrix_sdk_crypto/Cargo.toml b/matrix_sdk_crypto/Cargo.toml
index ea1fc330..509a3ee3 100644
--- a/matrix_sdk_crypto/Cargo.toml
+++ b/matrix_sdk_crypto/Cargo.toml
@@ -45,8 +45,9 @@ default-features = false
 features = ["runtime-tokio", "sqlite"]
 
 [dev-dependencies]
-tokio = { version = "0.2.21", features = ["rt-threaded", "macros"] }
-serde_json = "1.0.56"
+tokio = { version = "0.2.22", features = ["rt-threaded", "macros"] }
+proptest = "0.10.0"
+serde_json = "1.0.57"
 tempfile = "3.1.0"
 http = "0.2.1"
 matrix-sdk-test = { version = "0.1.0", path = "../matrix_sdk_test" }
diff --git a/matrix_sdk_crypto/src/verification/sas/helpers.rs b/matrix_sdk_crypto/src/verification/sas/helpers.rs
index 066d51f3..7934901b 100644
--- a/matrix_sdk_crypto/src/verification/sas/helpers.rs
+++ b/matrix_sdk_crypto/src/verification/sas/helpers.rs
@@ -318,13 +318,15 @@ pub fn get_emoji(
     flow_id: &str,
     we_started: bool,
 ) -> Vec<(&'static str, &'static str)> {
-    let bytes: Vec<u64> = sas
+    let bytes = sas
         .generate_bytes(&extra_info_sas(&ids, &flow_id, we_started), 6)
-        .expect("Can't generate bytes")
-        .into_iter()
-        .map(|b| b as u64)
-        .collect();
+        .expect("Can't generate bytes");
 
+    bytes_to_emoji(bytes)
+}
+
+fn bytes_to_emoji_index(bytes: Vec<u8>) -> Vec<u8> {
+    let bytes: Vec<u64> = bytes.iter().map(|b| *b as u64).collect();
     // Join the 6 bytes into one 64 bit unsigned int. This u64 will contain 48
     // bits from our 6 bytes.
     let mut num: u64 = bytes[0] << 40;
@@ -336,7 +338,7 @@ pub fn get_emoji(
 
     // Take the top 42 bits of our 48 bits from the u64 and convert each 6 bits
     // into a 6 bit number.
-    let numbers = vec![
+    vec![
         ((num >> 42) & 63) as u8,
         ((num >> 36) & 63) as u8,
         ((num >> 30) & 63) as u8,
@@ -344,7 +346,11 @@ pub fn get_emoji(
         ((num >> 18) & 63) as u8,
         ((num >> 12) & 63) as u8,
         ((num >> 6) & 63) as u8,
-    ];
+    ]
+}
+
+fn bytes_to_emoji(bytes: Vec<u8>) -> Vec<(&'static str, &'static str)> {
+    let numbers = bytes_to_emoji_index(bytes);
 
     // Convert the 6 bit number into a emoji/description tuple.
     numbers.into_iter().map(emoji_from_index).collect()
@@ -369,13 +375,16 @@ pub fn get_emoji(
 /// # Panics
 ///
 /// This will panic if the public key of the other side wasn't set.
-pub fn get_decimal(sas: &OlmSas, ids: &SasIds, flow_id: &str, we_started: bool) -> (u32, u32, u32) {
-    let bytes: Vec<u32> = sas
+pub fn get_decimal(sas: &OlmSas, ids: &SasIds, flow_id: &str, we_started: bool) -> (u16, u16, u16) {
+    let bytes = sas
         .generate_bytes(&extra_info_sas(&ids, &flow_id, we_started), 5)
-        .expect("Can't generate bytes")
-        .into_iter()
-        .map(|b| b as u32)
-        .collect();
+        .expect("Can't generate bytes");
+
+    bytes_to_decimal(bytes)
+}
+
+fn bytes_to_decimal(bytes: Vec<u8>) -> (u16, u16, u16) {
+    let bytes: Vec<u16> = bytes.into_iter().map(|b| b as u16).collect();
 
     // This bitwise operation is taken from the [spec]
     // [spec]: https://matrix.org/docs/spec/client_server/latest#sas-method-decimal
@@ -415,3 +424,62 @@ pub fn content_to_request(
         messages,
     }
 }
+
+#[cfg(test)]
+mod test {
+    use proptest::prelude::*;
+
+    use super::{bytes_to_decimal, bytes_to_emoji, bytes_to_emoji_index, emoji_from_index};
+
+    #[test]
+    fn test_emoji_generation() {
+        let bytes = vec![0, 0, 0, 0, 0, 0];
+        let index: Vec<(&'static str, &'static str)> = vec![0, 0, 0, 0, 0, 0, 0]
+            .into_iter()
+            .map(emoji_from_index)
+            .collect();
+        assert_eq!(bytes_to_emoji(bytes), index);
+
+        let bytes = vec![0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF];
+
+        let index: Vec<(&'static str, &'static str)> = vec![63, 63, 63, 63, 63, 63, 63]
+            .into_iter()
+            .map(emoji_from_index)
+            .collect();
+        assert_eq!(bytes_to_emoji(bytes), index);
+    }
+
+    #[test]
+    fn test_decimal_generation() {
+        let bytes = vec![0, 0, 0, 0, 0];
+        let result = bytes_to_decimal(bytes);
+
+        assert_eq!(result, (1000, 1000, 1000));
+
+        let bytes = vec![0xFF, 0xFF, 0xFF, 0xFF, 0xFF];
+        let result = bytes_to_decimal(bytes);
+        assert_eq!(result, (9191, 9191, 9191));
+    }
+
+    proptest! {
+        #[test]
+        fn proptest_emoji(bytes in prop::array::uniform6(0u8..)) {
+            let numbers = bytes_to_emoji_index(bytes.to_vec());
+
+            for number in numbers {
+                prop_assert!(number < 64);
+            }
+        }
+    }
+
+    proptest! {
+        #[test]
+        fn proptest_decimals(bytes in prop::array::uniform5(0u8..)) {
+            let (first, second, third) = bytes_to_decimal(bytes.to_vec());
+
+            prop_assert!(first <= 9191 && first >= 1000);
+            prop_assert!(second <= 9191 && second >= 1000);
+            prop_assert!(third <= 9191 && third >= 1000);
+        }
+    }
+}
diff --git a/matrix_sdk_crypto/src/verification/sas/mod.rs b/matrix_sdk_crypto/src/verification/sas/mod.rs
index 6ab639b6..ae6442bf 100644
--- a/matrix_sdk_crypto/src/verification/sas/mod.rs
+++ b/matrix_sdk_crypto/src/verification/sas/mod.rs
@@ -257,7 +257,7 @@ impl Sas {
     /// Returns None if we can't yet present the short auth string, otherwise a
     /// tuple containing three 4-digit integers that represent the short auth
     /// string.
-    pub fn decimals(&self) -> Option<(u32, u32, u32)> {
+    pub fn decimals(&self) -> Option<(u16, u16, u16)> {
         self.inner.lock().unwrap().decimals()
     }
 
@@ -464,7 +464,7 @@ impl InnerSas {
         }
     }
 
-    fn decimals(&self) -> Option<(u32, u32, u32)> {
+    fn decimals(&self) -> Option<(u16, u16, u16)> {
         match self {
             InnerSas::KeyRecieved(s) => Some(s.get_decimal()),
             InnerSas::MacReceived(s) => Some(s.get_decimal()),
diff --git a/matrix_sdk_crypto/src/verification/sas/sas_state.rs b/matrix_sdk_crypto/src/verification/sas/sas_state.rs
index 9b638bf0..4a382c6c 100644
--- a/matrix_sdk_crypto/src/verification/sas/sas_state.rs
+++ b/matrix_sdk_crypto/src/verification/sas/sas_state.rs
@@ -530,7 +530,7 @@ impl SasState<KeyReceived> {
     ///
     /// Returns a tuple containing three 4 digit integer numbers that represent
     /// the short auth string.
-    pub fn get_decimal(&self) -> (u32, u32, u32) {
+    pub fn get_decimal(&self) -> (u16, u16, u16) {
         get_decimal(
             &self.inner.lock().unwrap(),
             &self.ids,
@@ -667,7 +667,7 @@ impl SasState<MacReceived> {
     ///
     /// Returns a tuple containing three 4 digit integer numbers that represent
     /// the short auth string.
-    pub fn get_decimal(&self) -> (u32, u32, u32) {
+    pub fn get_decimal(&self) -> (u16, u16, u16) {
         get_decimal(
             &self.inner.lock().unwrap(),
             &self.ids,