diff --git a/ssh-key/Cargo.toml b/ssh-key/Cargo.toml
index 389e266..3ca3af6 100644
--- a/ssh-key/Cargo.toml
+++ b/ssh-key/Cargo.toml
@@ -80,6 +80,7 @@ p256 = ["dep:p256", "ecdsa"]
 p384 = ["dep:p384", "ecdsa"]
 p521 = ["dep:p521", "ecdsa"]
 rsa = ["dep:bigint", "dep:rsa", "alloc", "rand_core"]
+rsa-sha1 = ["rsa", "dep:sha1", "sha1/oid"]
 tdes = ["cipher/tdes", "encryption"]
 
 [package.metadata.docs.rs]
diff --git a/ssh-key/src/signature.rs b/ssh-key/src/signature.rs
index 50f0668..5b030d5 100644
--- a/ssh-key/src/signature.rs
+++ b/ssh-key/src/signature.rs
@@ -13,7 +13,6 @@ use crate::{private::Ed25519Keypair, public::Ed25519PublicKey};
 use {
     crate::{private::DsaKeypair, public::DsaPublicKey},
     bigint::BigUint,
-    sha1::Sha1,
     signature::{DigestSigner, DigestVerifier},
 };
 
@@ -32,6 +31,9 @@ use {
     sha2::Sha512,
 };
 
+#[cfg(any(feature = "rsa-sha1", feature = "dsa"))]
+use sha1::Sha1;
+
 #[cfg(any(feature = "ed25519", feature = "rsa", feature = "p256"))]
 use sha2::Sha256;
 
@@ -661,34 +663,54 @@ impl Verifier<Signature> for EcdsaPublicKey {
 }
 
 #[cfg(feature = "rsa")]
-impl Signer<Signature> for RsaKeypair {
+impl Signer<Signature> for (&RsaKeypair, Option<HashAlg>) {
     fn try_sign(&self, message: &[u8]) -> signature::Result<Signature> {
-        let data = rsa::pkcs1v15::SigningKey::<Sha512>::try_from(self)?
-            .try_sign(message)
-            .map_err(|_| signature::Error::new())?;
+        let data = match self.1 {
+            Some(HashAlg::Sha512) => {
+                rsa::pkcs1v15::SigningKey::<Sha512>::try_from(self.0)?.try_sign(message)
+            }
+            Some(HashAlg::Sha256) => {
+                rsa::pkcs1v15::SigningKey::<Sha256>::try_from(self.0)?.try_sign(message)
+            }
+            #[cfg(feature = "rsa-sha1")]
+            None => rsa::pkcs1v15::SigningKey::<Sha1>::try_from(self.0)?.try_sign(message),
+            #[cfg(not(feature = "rsa-sha1"))]
+            None => return Err(Algorithm::Rsa { hash: None }.unsupported_error().into()),
+        }
+        .map_err(|_| signature::Error::new())?;
 
         Ok(Signature {
-            algorithm: Algorithm::Rsa {
-                hash: Some(HashAlg::Sha512),
-            },
+            algorithm: Algorithm::Rsa { hash: self.1 },
             data: data.to_vec(),
         })
     }
 }
 
+#[cfg(feature = "rsa")]
+impl Signer<Signature> for RsaKeypair {
+    fn try_sign(&self, message: &[u8]) -> signature::Result<Signature> {
+        (self, Some(HashAlg::Sha512)).try_sign(message)
+    }
+}
+
 #[cfg(feature = "rsa")]
 impl Verifier<Signature> for RsaPublicKey {
     fn verify(&self, message: &[u8], signature: &Signature) -> signature::Result<()> {
         match signature.algorithm {
-            // TODO(tarcieri): optional off-by-default support for legacy SHA1 signatures?
-            Algorithm::Rsa { hash: Some(hash) } => {
+            Algorithm::Rsa { hash } => {
                 let signature = rsa::pkcs1v15::Signature::try_from(signature.data.as_ref())?;
 
                 match hash {
-                    HashAlg::Sha256 => rsa::pkcs1v15::VerifyingKey::<Sha256>::try_from(self)?
+                    #[cfg(not(feature = "rsa-sha1"))]
+                    None => Err(Algorithm::Rsa { hash: None }.unsupported_error().into()),
+                    #[cfg(feature = "rsa-sha1")]
+                    None => rsa::pkcs1v15::VerifyingKey::<Sha1>::try_from(self)?
+                        .verify(message, &signature)
+                        .map_err(|_| signature::Error::new()),
+                    Some(HashAlg::Sha256) => rsa::pkcs1v15::VerifyingKey::<Sha256>::try_from(self)?
                         .verify(message, &signature)
                         .map_err(|_| signature::Error::new()),
-                    HashAlg::Sha512 => rsa::pkcs1v15::VerifyingKey::<Sha512>::try_from(self)?
+                    Some(HashAlg::Sha512) => rsa::pkcs1v15::VerifyingKey::<Sha512>::try_from(self)?
                         .verify(message, &signature)
                         .map_err(|_| signature::Error::new()),
                 }