diff --git a/Cargo.lock b/Cargo.lock
index 800a8e4d..bed8c985 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -6679,9 +6679,9 @@ version = "1.0.1"
 dependencies = [
  "aes-gcm",
  "anyhow",
- "base64 0.22.1",
  "browser-signer-proxy",
  "common",
+ "data-encoding",
  "flume 0.11.1",
  "futures",
  "gpui",
diff --git a/Cargo.toml b/Cargo.toml
index 7a6bce9a..1cee8338 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -30,7 +30,7 @@ nostr = { git = "https://github.com/rust-nostr/nostr", features = [ "nip59", "ni
 # Crypto (NIP-17 encrypted file messages)
 aes-gcm = "0.10"
 sha2 = "0.10"
-base64 = "0.22"
+data-encoding = "2"
 
 # Others
 anyhow = "1.0.44"
diff --git a/crates/state/Cargo.toml b/crates/state/Cargo.toml
index 09dc9cd0..daebc7a9 100644
--- a/crates/state/Cargo.toml
+++ b/crates/state/Cargo.toml
@@ -26,7 +26,7 @@ mime_guess = "2.0.4"
 
 aes-gcm.workspace = true
 sha2.workspace = true
-base64.workspace = true
+data-encoding.workspace = true
 
 [target.'cfg(target_arch = "wasm32")'.dependencies]
 nostr-memory.workspace = true
diff --git a/crates/state/src/file.rs b/crates/state/src/file.rs
index b5926583..06ae44d5 100644
--- a/crates/state/src/file.rs
+++ b/crates/state/src/file.rs
@@ -1,11 +1,11 @@
 use std::path::PathBuf;
 
-use aes_gcm::aead::consts::U12;
+use aes_gcm::aead::consts::{U12, U16};
 use aes_gcm::aead::{Aead, AeadCore, KeyInit, OsRng};
-use aes_gcm::{Aes256Gcm, Nonce};
+use aes_gcm::aes::Aes256;
+use aes_gcm::{Aes256Gcm, AesGcm, Nonce};
 use anyhow::{Error, anyhow, bail};
-use base64::Engine as _;
-use base64::engine::general_purpose::{STANDARD, STANDARD_NO_PAD, URL_SAFE, URL_SAFE_NO_PAD};
+use data_encoding::HEXLOWER;
 use futures::AsyncReadExt;
 use gpui::http_client::AsyncBody;
 use gpui::{AsyncApp, SharedString};
@@ -130,20 +130,34 @@ pub fn encrypt(data: &[u8]) -> Result<EncryptedFile, Error> {
 
     Ok(EncryptedFile {
         data,
-        key: STANDARD.encode(key.as_slice()),
-        nonce: STANDARD.encode(nonce.as_slice()),
+        key: HEXLOWER.encode(key.as_slice()),
+        nonce: HEXLOWER.encode(nonce.as_slice()),
     })
 }
 
 pub fn decrypt(data: &[u8], key: &str, nonce: &str) -> Result<Vec<u8>, Error> {
-    let key = decode(key, 32, "decryption key")?;
-    let nonce = decode(nonce, 12, "decryption nonce")?;
+    let key = decode(key, "decryption key")?;
+    let nonce = decode(nonce, "decryption nonce")?;
 
-    let cipher = Aes256Gcm::new_from_slice(&key).map_err(|_| anyhow!("Invalid decryption key"))?;
+    if key.len() != 32 {
+        bail!(
+            "Invalid decryption key length: expected 32 bytes, got {}",
+            key.len()
+        );
+    }
 
-    cipher
-        .decrypt(Nonce::<U12>::from_slice(&nonce), data)
-        .map_err(|_| anyhow!("Failed to decrypt file"))
+    // Amethyst uses 16 bytes nonces, everything else uses the standard 12
+    match nonce.len() {
+        12 => Aes256Gcm::new_from_slice(&key)
+            .map_err(|_| anyhow!("Invalid decryption key"))?
+            .decrypt(Nonce::<U12>::from_slice(&nonce), data)
+            .map_err(|_| anyhow!("Failed to decrypt file")),
+        16 => AesGcm::<Aes256, U16>::new_from_slice(&key)
+            .map_err(|_| anyhow!("Invalid decryption key"))?
+            .decrypt(Nonce::<U16>::from_slice(&nonce), data)
+            .map_err(|_| anyhow!("Failed to decrypt file")),
+        len => bail!("Unsupported decryption nonce length: {len} bytes"),
+    }
 }
 
 pub fn sha256_hex(data: &[u8]) -> String {
@@ -168,6 +182,7 @@ pub async fn upload_encrypted(
     let sha256 = Some(sha256_hex(&encrypted.data));
     let original_sha256 = Some(sha256_hex(&data));
     let size = Some(encrypted.data.len() as u64);
+    let base_url = server.to_string();
     let keys = Keys::generate();
     let client = BlossomClient::new(server);
 
@@ -179,7 +194,20 @@ pub async fn upload_encrypted(
                 None,
                 Some(&keys),
             )
-            .await?;
+            .await
+            .map_err(|e| {
+                let message = e.to_string();
+
+                if !message.contains("415") {
+                    return anyhow!(message);
+                }
+
+                anyhow!(
+                    "{base_url} rejected the encrypted file. Encrypted attachments are uploaded as
+                     opaque data, which this file server does not accept. Choose a different file
+                     server in the settings."
+                )
+            })?;
 
         Ok::<Url, Error>(blob.url)
     })
@@ -311,20 +339,8 @@ fn parse_dim(value: &str) -> Option<(u32, u32)> {
     Some((width.parse().ok()?, height.parse().ok()?))
 }
 
-fn decode(value: &str, expected_len: usize, label: &str) -> Result<Vec<u8>, Error> {
-    let decoded = STANDARD
-        .decode(value)
-        .or_else(|_| STANDARD_NO_PAD.decode(value))
-        .or_else(|_| URL_SAFE.decode(value))
-        .or_else(|_| URL_SAFE_NO_PAD.decode(value))
-        .map_err(|_| anyhow!("Invalid {label} encoding"))?;
-
-    if decoded.len() != expected_len {
-        bail!(
-            "Invalid {label} length: expected {expected_len} bytes, got {}",
-            decoded.len()
-        );
-    }
-
-    Ok(decoded)
+fn decode(value: &str, label: &str) -> Result<Vec<u8>, Error> {
+    HEXLOWER
+        .decode(value.to_ascii_lowercase().as_bytes())
+        .map_err(|_| anyhow!("Invalid {label} encoding"))
 }