Polkadot is the only chain in the wallet that uses sr25519 as its primary signature scheme. Every other chain uses some variant of secp256k1 (Bitcoin, Ethereum, Cosmos) or ed25519 (XRPL, Solana). The choice is deliberate and worth understanding.
What sr25519 actually is
sr25519 = Schnorr signatures over the Ristretto encoding of the Curve25519 elliptic curve. Three things that matter:
Schnorr, not ECDSA. ECDSA is what Bitcoin and Ethereum use. It's deterministic only by convention (RFC 6979) and has historical CVE patterns around malleability. Schnorr is provably secure under standard assumptions, supports efficient batch verification, and natively allows signature aggregation.
Curve25519, not secp256k1. Smaller signatures (64 bytes), faster verification, immune to several side-channel attacks that hit short-key curves.
Ristretto encoding. A subtle but important detail — Ristretto strips the cofactor of Curve25519, eliminating an entire class of "small-subgroup" attacks. Plain ed25519 (which Solana and XRPL use) is almost the same, but ed25519 has known equivocation issues that ristretto fixes.
Together: sr25519 is what Schnorr signatures should look like if you designed them from scratch in 2018. The substrate framework adopted it for everything.
What this means for you
Your Polkadot key is not your Ethereum key, even with the same mnemonic. Different curve, different signature scheme, different public-key derivation. The wallet computes them separately:
XRPL mnemonic → BIP-39 seed → BIP-44 derive
├─ m/44'/0'/0'/0/0 → Bitcoin (secp256k1)
├─ m/44'/60'/0'/0/0 → Ethereum (secp256k1, but Keccak hashed)
├─ m/44'/118'/0'/0/0 → Cosmos (secp256k1)
├─ m/44'/354'/0'/0'/0' → Polkadot (sr25519)
└─ m/44'/501'/0'/0' → Solana (ed25519)
Six cryptographic primitives across nine chains, but all rehydrated from the one XRPL mnemonic. If you back up your XRPL seed, you've backed up everything.
The substrate path quirk
There's a wrinkle worth mentioning. The substrate ecosystem uses its own path convention, written //44//354//0//0//0 (with // instead of /). The BIP-44 path m/44'/354'/0'/0'/0' translates to the substrate form by stripping the leading m/ and replacing each <n>' with //<n>.
The wallet's signer module does this translation internally — you supply a standard BIP-44 path in config, and the substrate-interface library gets a substrate-form path at signing time. The two are equivalent at the byte level.
If you ever import a Polkadot mnemonic into a different wallet, make sure that wallet uses the same path. Some substrate-only wallets (Polkadot.js, Talisman) default to // shorthand paths that don't match BIP-44. Mismatched paths = different keys = wrong address. This is the #1 cause of "I lost my DOT" support tickets.
Why this matters when you sign
Schnorr signatures support provably-secure multisigs that ECDSA doesn't. You can aggregate N signatures into a single 64-byte signature that proves N people signed. Ethereum is moving in this direction (BIP-340 Schnorr on Bitcoin, BLS aggregates on Ethereum), but Polkadot has it native from day one.
The wallet doesn't expose multisig signing in iter-G, but the cryptographic foundation is there. If you join a 3-of-5 multisig on Polkadot in a future iteration, the signatures will aggregate. Your transaction will be one signature, not three.
What about Kusama, parachains, etc?
Every chain in the Polkadot ecosystem uses sr25519 (or, in a few cases, ed25519 — Substrate supports both). The relay chain, Kusama, AssetHub, Acala, Moonbeam, Astar, all of them. So a sr25519 key is genuinely portable across the entire ecosystem. The SS58 prefix differs per chain (we cover that next), but the underlying key material is the same.
The TL;DR
Polkadot uses sr25519: Schnorr signatures over Ristretto-encoded Curve25519. Smaller, faster, safer than the ECDSA you know from Bitcoin/Ethereum. Different curve from ed25519 (Solana/XRPL) but related. Your Polkadot key is independently derived from your XRPL mnemonic at BIP-44 path m/44'/354'/0'/0'/0'.
Next: how that key gets encoded into the 1… address you see in the wallet.